Celeron D, specifically the 2.53GHz one you have, is a Pentium 4 Prescott-based CPU with 256KB L2 cache and 533 fsb. Frankly, it's a slow processor. However, if you want to have some fun, you can pin mod that old Celeron to 800 fsb, giving you a 3.8GHz Celeron D. The stock Dell cooler SHOULD be able to handle it. Might need a voltage pin mod as well to make it stable at 3.8. If you have absolutely no idea of what I'm talking about, please disregard.
Also, don't go with the 6200LE shown to you in that link. It's obviously PCI express. You need the PCI-only card. I also recommend an 8400 or 9400 card, but actually, I recommend you swap out that Dell mobo and in place put in an AMD mobo with a 780G chipset, followed by a cheap X2 cpu and a gig of DDRII.