Go for an externally powered one (with its own power adaptor). It should be big enough (in GB). I shouldn't use any of the backup software that might be on it. And be sure you can easily get out the hard disk in case the electronics fail.
And yes, you can use it to transfer files from and to any Windows PC from XP upward. In that case (no Apple in the mix) format it NTFS, not FAT32.
Please could someone adise me I would like to get a Ext hardrive and would like to know what would be best, at the moment I am running with XP and was thinking that if I where to buy another PC with say 7 could I still transfer files or would that be a problem. If you could tell me what would be the best make to go for.
Thanks for any help Norwich City