Have a look here and also, afterwords, maybe use one or two of the following to make sure its gone: F-Secure On Line Scan -- http://support.f-secure.com/enu/home/ols.shtml
BitDefender On Line Scan -- http://www.bitdefender.com/scan8/ie.html
A-Squared On Line Trojan Scan -- http://www.windowsecurity.com/trojanscan/
House Call Anti-Virus http://housecall.trendmicro.com/housecall/start_corp.asp All the programs mentioned are for free.
Just as an FYI, in the future, you might want to post this type of question in the virus and security forum.
I am using windows XP and Grisoft AVG identified a trojan as "Generic XMS" on my computer. AVG could not disable or remove it. I tried several registry repair programmes but it is still here.
What is it and how do I remove it?