Yen,
Unless you have heavily treaded tires, I wouldn't necessarily worry about buying a new wheel. The trainer will accelerate tire wear, but not dramatically. Tires are not horribly expensive, but then neither is a cheap wheel from Nashbar. Having to change wheels, though not a big deal, may inhibit you a little from actually using the trainer at times. If you get the trainer, also get a front wheel stabilizing block, just a chunk of molded plasitc, which will lift the front a bit to match the rear when on the trainer.