Originally Posted by Chone

Your Hardrock is fine and for 600$ you can perform some really nice upgrades, first and foremost if you want new brakes get discs, otherwise just swap out the pads in your current Vs and tune them up properly (and straighten up your rim). For 150$ you can get Sun Rhyno Lite XL rims laced to XT disc hubs or something similar, for 70$ a piece you can get BB7s and for 50$ you can Speed Dial 7 levers, so for 340$ you could have a very sweet disc/wheel setup. That leaves you with 260$ for the fork, I would get something nice like a Marzocchi MX Pro, its currently goes for 230$ or so for the 2005 120mm version (at blueskycycling) or you could go with the 105mm MX Comp and get matching fork travel for your frame and save 20$. http://www.blueskycycling.com/cat-fork-accessories.htm

So yeah for 600$ you can get awesome wheels, awesome discs and levers and and awesome fork, although I would also look into getting new shifters and derailleurs (go SRAM for sure, something like X.7 would be awesome) but then you might also want to make the jump to 9 speed with a new cassete and a new crankset but you would need a new bottom bracket since your current one is square tapered... but that would be an upgrade for later (or you can cram it into your budget by getting deore hubs on some other cheaper rims, a cheaper fork and use your current altus levers or something).