Full suspension is absolutely useless for commuting unless you do some serious trails along the way, front suspension is close second. I don't have any suspension on any of my bikes because good suspension cost a lot.
Since you are commuting, no point of spending any money to suspension forks, check the commuting bicycle pics in the sticky, you will see very small amount of bikes with suspensions.
Your Gary Fisher Mamba is fine, just change the tire into some at most 1.5" wide.
Although I do have a racing bike that's pretty modern, I commute around town using a Trek Aluminum hardtail from 1992, the only modification is the slicks and fenders. That's it, and it's a $50 investment.
By the way, I'm 20 years old.
I like to add that for bikes with front suspension at $600 price point, some people actually switch the front suspension fork with a rigid one for commuting.
Here's what you need,
1.5" Slicks, look for Schwalbe Marathons, Tioga City Slickers (that's why I run), Continental Contact, etc.
Full fenders, from SKS, Planet Bike, if where you live constantly rains and snow. Don't go for the half-assed mudguards, not as useless as full fenders.
Lights if you are riding at night.
You can spend up to $100 for these at most.
Last edited by mrbubbles; 12-08-07 at 07:05 PM.