Windows XP not booting. Need DOS-based Virus Scanner - Help!

My dad's computer has suddenly stopped botting Windows XP (SP2) for some unknwon reason. I have tried SAFE MODE, LAST KNOWN working, etc..etc...
Disconnected all USB devices...still no cigar. It gets to the Windows LOGO and about 20 seconds later, as it is supposed to get to the desktop, it just reboots.

I went into the BIOS and all looks okay.

I will try to run the REPAIR utility from the Windows XP CD the next time I am over there, but in addition, I want to run a VIRUSCAN in case some gremlin go into the system.

What VIRUS/SPYBOT program do you recommend that has the option of creating a DOS_BASED BOOT CD that will run SCAN from the CD-ROM?

Remember, since I cannot boot WINDOWS, only DOS-based will work for me.

Any advice is much appreciated!

P.S. I already have a DOS-BASED MEMETEST utility, so I am set on that one.

Try Risers method.

If the chkdsk returns too many errors its time to buy a new drive. Keep in mind the age of the MB, it may not support mega gig drives.

Did the computer have anti-virus loaded? So far the TrendMicro 2008 has the best software for me. When you first start the program, it will find any crap out there so starting in dos is really not the trick. Dos is 16 bit and most viruses are in the 32bit class anyway. The last version runs much better than 2007 and you get three loads per software key. Win XP sp2 or greater. It caught several viruses trojans and adware compaired to norton/spybot.
Worth the money!
Once up, you need to backup using a ghost program sending to a external drive.