Problems with Mac users on hotspot

We have had a ongoing problem with the Mac users on are hotspots. The speed is so slow I think you could slap a stamp on an envelope and get it there faster.Web, email, ftp it all has the same slow speed. We have had this problem with 2.7 and 2.8. Any ideas?

i am using a few macs with wireless connections to mikrotik routers. mostly 802.11b but did some 802.11g (only) testing.
performance as awaited, but the mt was configured as bridge AP, not as a hotspot.

my (old) airport card does not work with mikrotiks 802.11b/g mode.

(btw. if the macs are still on mac os 9, this could be the problem)

bye.
matthias