Calibration is using a 'test disk' to basically make sure the colors, brightness, contrast, etc. are 'optimal' both for the TV and your viewing conditions. You can hire someone from, I think ISF [Imaging Science Foundation?] to come and professionally calibrate, but that runs a couple hundred bucks at least. That of course is the 'best' way to go, but rather expensive.
You can also buy DVD's that help you self-calibrate based on test images on the disk. Avia, Sound and Vision, and Digital Video Essentials are the most popular ones. I know you can order DVE from Deep Discount DVD, it was under fifteen bucks when I ordered it. Amazon should have Avia and maybe DVE also.
When you go into a retail store to check out an HDTV or an RPTV, those tv's have to compete with every other tv on the floor, and those bright-ass fluoroscent lights, which is definitely not an actual home-type viewing environment. So they crank the brightness and contrast up on the floor models, so they stand out. Especially for RPTV's, and probably plasma also, this is bad--this, combined with static images, results in a relatively poor quality picture, and an increased chance of burn-in [which you do NOT want.] So, side note, never buy a 'floor/demo model' RPTV or plasma tv; there's no telling how much life is left in it, and it's not worth saving the couple hundred bucks.
Convergence applies to RPTV's, I don't think it applies to plasmas. An RPTV works by having the light guns in the tv shoot the picture onto the back of the screen. If the guns aren't converged, you'll have a misaligned effect, the red gun will shoot its image slightly to the left of the blue, which is slightly to the left of the green [or something like that]. Basically this adds fuzziness in the lower stages, and makes the picture look like crap if it's really misaligned. Most RPTV's should have an automatic or manual convergence option from one of the menus, that gives you a test image and allows you to 'focus' the guns so they're all aiming at the same points. Kinda like an out-of-focus binoculars; it looks like you have two images that are slightly offset to one another.
I unfortunately don't know much specific about plasma tv's. And if you've got up to a grand to spend on a DVD player and sound system, you don't want my advice [my 'home theater' and dvd player cost 350 combined, one was on sale and I had a gift certificate, but still. My setup is very consumer-entry-level, but it works for me.]
However, regarding a dvd player--you definitely want to look for one that is progressive scan. With an HDTV, it should display 480p, 480i, in addition to the higher resolutions, and anamorphic dvd's on a progressive DVD player in 480p mode really will show off your tv [until you get HD tv signals, of course.] You'll probably need component cables with a dvd player also.
Anyway, my complete setup is a Kenwood HTB-503 or 505 [i forgot] home theater in a box; Panasonic F65k 5 disk progressive scan dvd player; and Philips 60PW9363 60" HD-ready RPTV. I'm using Time Warner's Scientific Atlanta 8250, I think, HD cable box to get HD locals, HBO, Showtime, Disc, and I think one more. No, my setup isn't a showroom demo, but it was also bought piecemeal over about three years.
If you plasma has a built in tuner, you should be able to hook up an OTA antenna to go ahead and get over-the-air HD signals. If you don't want to go that route, make sure you ask your cable co. for an HD box.
I'm not into football, but I'll admit, football and hockey events look SWEET in HD.