Wireless network - PC, Mac & cable modem

I'm planning a wireless home network to include the following:

desktop pc, laptop pc, Apple G5 Imac, Telewest broadband cable modem.

Wireless network cards: I plan to install an internal PCI device for the
desktop and use a PCMCIA card for the laptop.

What do I need for the Imac? Do I have to buy the proprietary Apple
'Airport' network card (around fifty pounds) or can I get away with using an
external USB2 standard plug-in network card, which is only around twenty
seven pounds?

Speeds: I was thinking about Wireless G (54 kbps) although I see that there
are some non standard systems that run faster than this - up to 108kbps
(Super-G/MIMO).

Is there any point in installing one of these faster systems or is it better
to stick to the standard Wireless G, and would a faster system work in the
Imac anyway? If not, presumably the Imac would slow down the whole system to
54kbps?

One MIMO system which looks interesting is the Belkin F5D9016uk Pre-N MIMO
Wireless Broadband Router - nice and fast and backwards compatible:

http://www.broadbandbuyer.co.uk/Shop...ProductID=2235

Any comments on this or other types of broadband router appreciated.

Are there any issues I should be aware of when networking PCs and a Mac?

Thanks in advance.