Someone in this board had the nice idea of emailing the file to yourself. I don't know how that would work if your computer died though...
Just get a little flash drive thing, a 2GB one is so cheap they're practically giving them away. Well, $15. Probably closer to $85 in Aussie though 
Gmail can hold around 7+ GBs now, I remember when it was 2 GBs and invite only.
And unless you have Outlook Express (or equivalent) downloading your Emails and then deleting them, the file will stay stored on Google's Email server.
(You need to make a stickie called, "How To Backup Your CoD4 PROFILE")
Go to
My Computer (XP) or
Computer (Vista/7) and then to the hardrive you installed it on, most likely C:\ (It's the default.) and open the folder called Program Files then Activision then Call of Duty 4 - Modern Warfare then players,
Or copy and paste this into your Start Search bar, C:\Program Files\Activision\Call of Duty 4 - Modern Warfare\players
now make a zip file of the folder called "profiles" open your browser and then go to you email account and start a Email message and then upload the zip file you just made, and email it to yourself.
