The office where I work uses a small wireless network. We have anywhere from 10 to 20 people connecting at once, and since we have to use AT&T Slow as Molases DSL High Speed DSL, our connections blow and the internet is constantly bogged down. Unfortunately we're ineligible to use U-Verse, so 5mbps DSL is the best we can do now (aside from a hardwired T3 connection from the studio lot, but they charge us an arm and a leg for it).

Would upgrading our wireless router make a great difference, or are we just screwed?

At the moment we're using a Netgear RangeMax with a Linksys Wireless-G Access Point.

Changing routers will probably not make much difference.
Make sure the router is set to use one of the lesser-used channels (e.g. 3, 6 or 9) to minimize interference.
If you're using both of those routers like implied, make sure they are using dissimilar channels (so 3 and 9 would be a good bet)
Is there no cable internet available?

Not really. We're on a studio lot (I work for a TV production company) and they're very against us even having DSL.

My netgear rangemax wpn824 constantly loses connection. Nobody in netgear has a good explanation for it. From what I hear, the WTR54g is the greatest router ever, especially if you flash tomato or DD-WRT or whatever on it.

I think we went from a Netgear to another Netgear and both suck. Unfortunately I can only recommend what to get rather than just make that executive decision, so I'll definitely mention the WTR54g, thanks.