I would recommend that you get 54g 802.11g wireless equipment, as data transfer is much quicker.
Netgear is in my opinion the best make for networking equipment but it can be very expensive.
Belkin is also a very good make and is also cheap to buy.
It will be better if you buy a WiFi Router, and 2 WiFi PCI cards for the computers as your internet connection will be unaffected if any main computer is switched off.
512kbps is about 1% of your 54Mbps, so quality is definately not affected. In fact it is better than wired Hubs/Switches/Routers of similar price because they normally are around 10Mbps.