I'll link to my thread where I had issues setting up reaper on my laptop too as some of the stuff could help you even though my laptop has different hardware to yours but still worth a shot:https://bitcointalk.org/index.php?topic=93764.0
Basic steps for reaper:
1.Download and make sure you are using the latest reaper as it's less buggy than v12 (this fix works on my 2 systems)
2.I presume you wish to mine LTC (litecoins) with GPU
3.Open the reaper.conf file and remove these 2 lines from reaper:
b.save and exit in notepad or your text editor of choice.
4.Go into you litecoin.conf and modify:
a.your pool host (e.g litecoinpool.org)
b.then port (usually 9332 but can differ with other pools)
c.username (of your miner/worker)
d.password (of your miner/worker,not your account login for that pool,ok)
5.Run reaper.If this is the first time you run reaper successfully,it'll compile a binary suitable for your GPU and settings in reaper.Be paitent as this can take a while.
6.Once reaper finishes compiling itself and is successfull,it'll start mining.