You're probably going to want to listen to Oscarbreeder on whether or not to use this filter. It is, indeed, an outdated technology. Theoretically, the undergravel filter provides an active biological filter beneath the gravel. However, realistically, it is a poor mechanical and chemical filter that must be cleaned out in a very labor-intensive way every couple of months. You wouldn't believe the amount of waste that forms under the undergravel plate in just a few days!!!
ppl on this site generally recommend hang-on-the-back filters, especially to ppl who are knew to the hobby. The best of these are undoubtably the penguin/emperor line manufactured by Marineland. The penguins are cheaper, but have biowheels, an excellent medium for biological filtration (i.e. the bacteria that break down harmful waste such as ammonia, nitrite and nitrate produced by fishes in your tank). The emperors are slightly more complex, and add a more sophisticated system that guarantees the biowheels never stop moving. The emperors also offer more room for any additional media (e.g. peat, crushed coral, ammonia-reducing packs) you may want to use to change various parameters in your tank.
If I were you, I'd buy and emperor or penguin filter appropriate to the size of tank you buy (if you're still willing to buy the tank after finding out that your present equipment is not rockin'...). A 10 Gallon tank would best be filtered by a Penguin 125 or a Penguin Mini (on the low side). A 20 Gallon by a Penguin 125 or an Emperor 280. A 30 Gallon by an Emperor 280 or a Penguin 330 (slightly overkill, but not really; I filter my 29s with these). A 55 Gallon with an Emperor 400 (this is what I have on my 55), or possibly 1 or 2 Penguin 330s. These numbers all signify "flow-rates"--the number of gallons per hour moved from the tank into the filter and back into the tank. An ideal flow rate is between 6 and 15 times the volume of the tank, and depends on the number and size of fish in your tank.
There are a lot of fantastic sites on the web. Read as much as you can, and ask us all the questions you come up with. A good site for simple and complicated questions is www.thekrib.com
(as in the Kribensis Cichlids of Africa). I'm blanking on other good resources. It'd be helpful if anybody else posted any pertinent sites... Also, feel free to PM (personal message) anybody. We're a pretty friendly bunch.
Hope this helps. Also