mssys.exe help me please

Help please...I have a XP pro system and I now have a trojan or something like that..mssys.exe is in my windows directory...my av tells me i have backdoor ds...but it cant get rid of it. Shut down sys restore rebooted then looked in the reg under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and its not there. now that i've shut down sys restore I cant backup to a know good date nor can i delete it.. it wont let me. My system is running very weird now..my cursor ends up blinking out to the hour glass like something is trying to run but what I dont know...what can i do..please help
thank you

 

See how you go over here.

 

you could also head here

http://www.majorgeeks.com/download.php?id=29

and try one of the various trojan removal tools.