I have the solution to the problem of getting you wallet from windows to linux (not the online)
after fighting with it all day and finally figuring it out,
if it helps anyone and they want to reward me (not expecting anything),
My address is 12fuR1FF753m9E5PKiK6wU7RSHX23WoQng
Install Bitcoin
(assuming you have a copy of your wallet.dat file first in a safe place)
delete the contents of your bitcoin directory (it's a hidden directory so you need to enable view hidden files)
Ubuntu = Home\.bitcoin
Windows XP = C:\Documents and Settings\YourUserName\Application data\Bitcoin
Vista/7 = C:\Users\YourUserName\Appdata\Roaming\Bitcoin
Dissable all network connections
Start the bitcoin program
Once it's finished loading, close it.
Now copy your wallet.dat file into the bitcoin directory
Enable your internet connections
Start the bitcoin program and it will work
(You can see your old wallet addresses and the blocks start downloading without giving an error.)