Hi, and welcome to the forum. As scifan said, you can easily go to and jail break that iPad1 on iOS 5.1.1.
I'd just like to add that I recommend you do a backup before upgrading so you can get all your stock iPad stuff back after you upgrade. That way, you'll still have your app data (e.g. game progress), settings and so on.
Then, right after you upgrade (restore from NEW at the start), go ahead and jail break it BEFORE you put anything back on it. It is my opinion/experience that jail breaks work best on near empty iPads.
After the jail break, use the "restore from backup" function in iTunes to put the backup in the iPad. iTunes will do its magic and you'll be all set.
I would not commend using any backup program for your Cydia tweaks. Given that you are coming from a much older iOS, my recommendation is to make note of which ones you have, upgrade to iOS 5.1.1, jail break and then go put the tweaks on in small numbers. That way, you can ensure tweaks will still work with the new iOS.
Good luck on your upgrade and let us know how you get on.
Marilyn
P.S. And, since you talk about a jail broken iPad, I've taken the liberty of moving your post over to the Hacking section. Thanks for your understanding.