[MarineHawk]

Thanks for all the advice. Based on the below, any further advice would me much appreciated.
Backround: I have windows XP on a PC laptop. I've been having trouble lately sometimes when I turn on the puter, and a message about an error with a system32 file comes up. If I reboot, sometimes more than once, it will eventually work fine.
Update: I started out with the Trend Micro free thingy last night. It went through step #2 whereby it identified about a dozen viruses - all some permutation of a Trojan Horse virus. When I progressed to step #3, cleaning the viruses, I got some kind of error message saying something to the effect that there was an "addition" named HouseCall (the Trend software), and Internet Exlporer must shut down.
Upon shut down, and multiple rebootings, the same thing occured: When i got to the beginning of step #2, an error would come up and say that Internet Explorer must shut down. This happened at least 6 times at precisely the same level of progression.
Not to be deterred, I downloaded the AVG free stuff. After I realized, though there is no message to this effect, that one must reboot after installing any upgrades to that software, I rebooted, and launched it. It swept through my entire puter and identified 11 files corrupted by the Trojan thingy. These files appear in a list of some kind. When I highlighted and right clicked on all of them, the option "Heal" appeared. I clicked it. Then all of the red icons next to these files turned into some other non-red thingy, apparently indicating that they had been "healed." After saying some sincere puter health prayers, I went to bed at the late hour to which all of this had brought me. This morning, I restarted the puter, and an AVG window came up stating that the Trojan Horse was in this file: C\windows\system32\wxtwdx.sys
Then, when I press "Heal," it says that it cannot to so, access to the above named file is "denied."
Any suggestions?
Thanks again.