Unfortunately this is common with linksys routers, the firmware released with the router is usually buggy and even the updates don't fix all the problems or create new ones.

You could either wait until linksys post a fixed firmware update on their site (could be some time, being that I couldn't find WRT54G v7 on their US site) or you could try a third party firmware.

The latter is probably the best option as there's more likely to be continued updates and a support community. The only problem is it's unsupported by linksys and you could void your warranty or brick your router (when an upgrade fails and you're unable to recover/restore it).

have a look at:
DD-WRT - Wikipedia, the free encyclopedia
WRT54G - Wikipedia, the free encyclopedia