Hi Tim, I'm not sure if you're talking about printing them yourself or by using one of the online photo shops. Personally I use an on line service and simply crop the image for the aspect ration I'm looking for. Most services provide resolution guidance (so you don't upload something that just won't print well at the requested size) but basically use the highest resolution possible. Also, some of the services allow for you to upload tifs so you don't have to worry about compression artifacts (though you can save as a jpg at 1% and not have a problem). I've had prints done as large as 20 x 30 from my digital rebel (6 mp) so I see no reason you should have any trouble at all with large prints (11 x 14 or more).
There are a number of online shops out there and I haven't tried them all but I've used
shutterfly,
dotphoto and
ezprints among others with quite satisfactory results. Currently I'm using
mpix. Mpix is a tad more costly but their quality is top notch (IMHO).
Oh, and if you want to try one of those 20 x 30 inch monsters try
Elco, the price for their "internet special" is great at $9.95 for one (you have to buy two but even with shipping you can't beat it...

). I've been quite happy with them.