For Starters you are going to need two more WRT54G Routers, as they can't function as an Access Point and in Client Mode at the same time.
Not quite
Firstly, in the client/AP setup suggested, only one extra AP is needed, the client side will need nother AP, but the AP end of the connection can still serve many clients(laptops etc)
the cheapest solution though is WDS, its just a matter of whether or not the indoor equipment will get spillover signal from the outdoor directional antennas.
remember, when swapping out the standard antennas for longrange, its advisable to disable the other antenna, the 2 in combo is only good for diversity, ie where both cover the same area, if both are left enabled, it will result in packetloss
basic concept : WDS allows a AP to speak to another AP while serving wireless clients.
it will not give an optimal connection, it halves the throughput between the 2 AP's, remote clients should in theory still have max speed.
choose your AP's wisely, as some don't have functionality fo WDS, in this case, 2 WRT's can do ANYTHING the radio permits them to, if you have the right knowhow, and don't mind getting your hands a little dirty in commandline.
firmwares that are capable, are openWRT, DD-WRT, and sveasoft, personally, I'll stay away from the latter 2, and go openwrt, I find them both bloated and buggy, but then again, I don't mind a shell and vi.
Have you been to Jawug.za.net yet, very valuable source, and good to put your network to greater use, theres guys there that have been doing this for years, and can also be invaluable in such a setup, I know, coz I've just been thru it/going thru it now.
If anyones interested PM me, just got a network off the ground in Lonehill, that will link to sunninghill by the end of the month!