Safely checking external drives

Hi, firstly, I want to say thank you, as someone who has never had to post, bu has used other people solutions in that past, it is greatly appreciated.

Now, my issue.

I have a computer, and a wide selection of hard drives. For some reason, I was using my computer with just my 160gb C drive on, and a USB stick attached.

I then got an avira alert that I was infected with ramnit.c, I tried to go through some of the solutions, they weren't working, and, to be honest there wasn't anything important on the hard drive, so I just reformatted it, and reinstalled windows.

My problem now is, I have a USB stick I am pretty sure is infected (i have a week old back up on my laptop, but would like to recover the files from the last week if it's possible). And several external harddrives, that if my antivirus took time noticing the infection, may be infected.

My question is, how can I safely check, and if needed fix these drives, without risking re infection? I am currently using windows XP, and have a laptop (on windows 7) as well if that helps.