1st of all, do u see that regscan.exe thing only in the Task Manager or there is a regscan folder as well ??
If its the folder, and u cant delete it, then u should try in safeboot mode., logged in as an administrator. 
This is how u go to safeboot mode :
1. CLick start, then Run
2. Type in msconfig, and press OK
3. Choose the BOOT.INI tab on top, and then tick the /SAFEBOOT box.
4. After that, restart ur system.
NOTE : Everything seems different in safeboot mode. So, dont be surprised when u dont see any graphics. Log in as an administrator, locate the folder and see if it deletes.
To go back to normal mode, simply follow steps 1 and 2, then just uncheck the /SAFEBOOT box, restart ur system.
Hope this helps.
I think it's F8 or F12 when the computer boots
yup, its the F8 key. But u can enter safeboot mode either way.