I bought a Belkin Range Extender and it was absolutely useless in that function. It was so deaf that it didn't extend range.
I have come upon a donated Hewlett Packard Procurve 530 Access Point. It is a *very* fancy box, but I have not used the features which would probably solve Cameronian's problems. The 530 contains two complete wireless sections, both of them with diversity and can use either built-in or external antennas. One of them is a usual 802.11b/g WiFi. The other can be configured for 802.11 a or b/g.
The key feature is that these boxes can be configured so that one of the wireless sections can be used as a bridge to additional 530s to make a large and complex wireless network. Presumably you would use the 802.11a RF section as the link to further Procurve 530 boxes some distance away.
Need I tell you that the Procurve 530 costs about ten times as much as a cheapo Belkin access point? It seems to be a professional-grade product.
[My purchase of the Belkin Range Extender wasn't a complete loss, since I now use it in its 802.11 b/g WiFi Access Point mode.]
seacue