Is there a way to free my computer of viruses without having to download any more programs?

i have tried uninstalling many unused programs through CCleaner, which kind of helped increase its speed. i also installed McAfee antivirus, but for some reason, the on-access scan never finishes scanning my computer entirely; it always freezes at a file called Symaddlin.dll (or something similar?). i think the real problem is at startup; it's REALLY slow. it also doesn't start it in safe mode; instead, a flurry of commands (in MSDOS format) bombards my screen. i have a sony vaio with windows XP media center 2005. i'm trying to find a way to clean my computer without installing any more programs; i mean, some of them really help, but i just don't want anything more to attach itself to the laptop's harddrive/memory. i also don't really want to completely reboot the system/erase everything and start over, it's kinda a hassle, but it's my last resort. please help, i'm not much of a computer person D: and i really need to get my computer working ASAP, i have physics and calculus HW due LOL

Is there a way to free my computer of viruses without having to download any more programs?downloads

It sounds bad to me. This is the reason I don't use laptops. I keep my OS (operating system) on one drive and my files on another. That way if I run into a problem I just wipe the drive with the OS and all is well with the world again.