One has to make an assumption about bitcoin exchange prices going forwards. 

On one hand BTC could be 100 USD in the fall and miners will easily pay back investments made today.

On the other hand its more likely that BTC could be about 20 USD and investments made today would not pay back, given sunk equipment cost, effort spent configuring, troubleshooting and monitoring the rigs, electricity cost of the rigs plus air conditioning cost.

At various points in the history of bitcoin mining its been more profitable to forgo mining and simply purchase the coins at market with equivalent funds for hoarding.

When you get low MH/sec the likely cause is the miner software defaulting to CPU mining when the GPU card is not found, not initialized or so forth.

This happens to me on my dual HD 5770 rigs occasionally and I perform a power-off/on reboot.

AMDOverdriveCtrl -h

will display the graphics cards.

aticonfig --list-adapters

will do the same.

The Sapphire HD 5770 GPUs are relatively quiet.  Ordinarily they run at 172 MH/sec but when overclocked to 960 MHz and with poclbm -w 128 they yield 202 MH/sec.

I've had trouble using AMDOverdriveCtrl over ssh because of X forwarding.   I worked around the issue by configuring my GPUs from a startup.sh shell script that is named in /etc/rc.local in my linuxcoin OS.

Relevant lines in the startup.sh script are tailored for my 5770 GPUs ...

DISPLAY=:0.0 aticonfig --od-enable
DISPLAY=:0.0 aticonfig --od-setclocks=960,0 --adapter=all
DISPLAY=:0.0 aticonfig --odcc --adapter=all

Try the Bitcoin Faucet at ...

http://freebitcoins.appspot.com/getsome

The Newegg HD 5830s are out of stock and will probably remain that way.   I went with six overclocked 5770s on three motherboards and am happy with 1200 MH/sec drawing 860 watts from a shared UPS.

On linux I can overclock my HD 5770 cards to 202 MH/sec 960 MHz.  I use poclbm with -w 128.

linuxcoin is my OS and I have a startup script ....

DISPLAY=:0.0 aticonfig --od-enable
DISPLAY=:0.0 aticonfig --od-setclocks=960,0 --adapter=all
DISPLAY=:0.0 aticonfig --odcc --adapter=all

cd /opt/miners/poclbm

./poclbm.py -d0 --host=uscentral.btcguild.com --port=8332 --user=XXXX --pass=YYYY -v -w 128 &

./poclbm.py -d1 --host=uscentral.btcguild.com --port=8332 --user=XXXX --pass=YYYY -v -w 128 &

Back in July 2010, I generated two blocks all by myself before rising difficulty forced me out of CPU mining - as there were no pools back then.

Now I hope to keep mining coins with my GPU rigs until the earnings are less than my daily 1.74 USD electric bill for the 850 watts I consume to yield 1200 MH/sec - September?

I run three rigs without cases ...

Each motherboard has two HD 5770 overclocked and each yields 202 MH/sec with poclbm -w 128.  The total MH/sec is about 1200 and the shared UPS draws 860 watts.  Because I use linuxcoin I have no hard drive - just a USB flash memory stick.  The rigs run rather cool considering their hash rate and I put them in the non-air conditioned crawl space under my Austin Texas house where the ambient temperature is a steady 30 C.

My choices were limited when I bought the GPUs and the HD 5770 seemed optimal at the time.

You might have to settle for the readily available, as of late June 2011, HD 5770 GPU cards.  Mine do 202 MH/sec when overclocked and work = 128.  They do not run too hot.

Here in Austin Texas I subscribe to the local utility's Green Power Program, e.g. wind turbine, and pay $ .085 per KWh.  My mining rigs operate at a total 1200 MH/sec and the shared UPS draws 860 watts.

I run chrome and found the site unreadable - sorry.

It took a few days for traders, merchants and miners to move funds and bitcoins to TradeHill.  Volume picked up only today.

When Mt Gox gets back online, prices may firm up, provided that the site exhibits solid security.

Space heaters - ha ha.

Right.  FAT32 is a proprietary Microsoft format and you need to perform that operation on a windows device.  When I got linuxcoin working, thats the only step that needed Windows.

Try dropping your AGGRESSION to 8 or below. 

Also I found that poclbm was more stable and ran cooler for own three rigs having six overclocked 5770s running at 60-70 C.

I have three case-less motherboards with two overclocked 5770 cards apiece.  The shared UPS draws 860 watts.  The cards are from two different vendors - the Sapphire cards run 10 C cooler, i.e. 60 C and the others 70 C.  I situated them in the crawl space under my Austin Texas house where the ambient temperature is a steady 30 C, despite outdoor temperatures climbing to 38 C (100 F).

They run great with the exception of one Sapphire card which I cannot overclock.

I chose a Radeon HD 5770 GPU from Newegg a few weeks ago, as it was the most cost-effective card that they then had available.  When overclocked it gets about 202 MH/sec and I have six of them in three rigs that total 860 watts power draw.

Desktop computers are dropping in popularity compared with the iPad, netbooks, laptops and smartphones.  But one real advantage of the desktop, i.e. tower configuration is that multiple full size monitors are supported.

The AMD GPU cards that are great for bitcoin mining also support up to six monitors - the eyefinity feature.
http://www.amd.com/us/products/technologies/amd-eyefinity-technology/Pages/eyefinity.aspx

I'll hang on to one or more of my Radeon HD 5770 cards to use for multiple monitors, after bitcoin mining becomes unprofitable at my electricity rates.

Given that you accept that mining will not have a pay-back at current bitcoin exchange prices, I offer that you might enjoy learning about Linux with your mining rig.  The linuxcoin OS boots from a 2GB USB memory stick and you do not need a hard drive.  The linuxcoin forum thread is very active - perhaps you can configure a dual-boot after you get Windows running to your satisfaction.