The T3i does have an articulate screen if that is something you are interested in, and I believe a bit better fully auto AF, but those aren't necessary. As far as your old lenses go, they will not work right out of the box. Canon and Nikon went different routes when they went digital (actually not digital, but AF I suppose). All DSLR Canons have AF with the EF and EF-S lenses. Nikon has certain bodies that have motors built into the bodies and those that do not. If you want AF with Nikon, you have to determine which body you have and if it has the motor built in or if you need a lens that has the motor. Not really important since I don't believe your lenses have AF anyways. Your lenses can work with an adapter, though you will lose EXIF data information. Not a big deal. And of course you will have to manual focusing.
There is a magnification factor when using the adapter and the newer lenses do have better IQ, but that is only if you are worried about having the best IQ which is also creative decision. I am not sure how easy to find the adapters are, but i have heard ebay is a good place to look.
In short, if you want to use your old lenses you can, and the T3 is a good body, to start for digital. It doesn't offer as good of controls you get starting with the xD bodies, but I am not sure that is a concern of yours. You will get a max native ISO of 6400 which is not bad at all. Depending on what focal ranges you are interested in, there are pretty good cheap lenses that will not require the adapter, and supposedly you might be able to get a good return on the FD mount lenses some places.
Canon took mixed reviews when abandoning the FD mount, but I have heard that overall quality jumped big time because of it. Not sure this is the info you wanted to hear, and I am not expert about the FD mount lenses. but from my research on Canon, cameras in general, and personal knowledge, that is the case. I'll do a bit more research and update this, and maybe someone who has had experience with FD to EF/EF-S lenses can jump in.
EDIT: You will pretty much have to be in manual mode (I only shoot in manual, and if you were using FD mount lenses, that should be what you are used to). The downsides are no EXIF data about the lenses (who cares?) and the slight magnification (still looking into what that amount is exaclty). The T3 will have a 1.6x magnifciation on it to begin with, so you lenses will not appear as wide as if you were shooting on 35mm. Last, depending on the brand of the mount, you could see a variable amount of loss in IQ On the plus side, you can still use your FD mount lenses.