You will get a lot of different opinions on this topic...

I assume your router is actually a WRT54G (not 64G?)...which is a very popular router and should work fine with Slingbox (mine did).

Before you buy a new one, have you made sure you have the latest firmware for the router?

If you have an earlier version of the WRT54G (v1 - v4), there are numerous 3rd party firmwares available that are arguably better than the factory's.

If you are looking for a new router, I have set my brother's Slingbox up with a $30 Netgear WGR614, which has worked perfectly for a year now.

My personal favorite currently are the Ubicom Stream Engine equipped routers. This is a hardware QoS chip that several vendors incorporate into their designs. I use the inexpensive Zyxel X-550, and also own (as a spare) the identical Trendnet TEW611BRP. The QoS ensures my VoIP phone lines aren't affected by streaming my Slingplayer outside of my LAN. D-Link also makes a series they call Game Lounge that incorporate the Ubicom QoS.