If you made a backup of your trainers prior to installing a new OS, you can restore the copies you have on your new Windows installation. You will have to log into Cheat Happens on your new installation or download a new offline key prior to using them. If for some reason they don't work then yes you would have to redownload them.
Additionally, you may have multiple copies of the trainer on different computers for your personal use only.
[Edited by Neo7, 2/26/2011 3:28:18 PM]
Ok, so all I need to do in relog on here? (already done sice i posted the question) and I figured id have to make a new offline key.
Thanks for the quick responce!