Always a very tempting idea to start from scratch, it conjures up images of a brand new start, and that's what it is. But like you I'm not an advanced user, and whenever I format a hard drive I allow a day and a half for the process. Be aware of everything you have to reinstall, anti-virus programs, email programs (do a search on how to save emails in Outlook Express if you want to save anything in that line... it ain't simple) etc etc. If you have software discs for everything you want to reinstall and you're confident you can handle everything including reinstallation of broadband/dialup connections, networking etc, then go ahead.
You may find it's more worthwhile going through the hijack processes as described in various threads here (search on HJT for a start). You can free your computer of all the nasties without necessarily taking the drastic step of reformatting. AdAware, Spybot, HJT, all the usual suspects. Download them all and use them before you reformat, you have nothing to lose.
And if you have to format, do another search on saving. It's unbelievable what you can lose from a hard drive without even knowing it's there until you start from scratch.
And since you're using XP, don't dismiss the restore function. If your nasties are relatively recent, it's well worth snapping your fingers and taking your computer back to a time when things were better!