Increasing Wireless Signal Strength: Booster or Antenna?

Although the WiFi (802.11b/g) hotspot isn't so far away (less than 50
feet), by the time it's reached the machine in question the signal's
dropped to anything from 25 to 50 percent... 50% is tolerable; 25% is
slooooow!
The access point is a Netgear WG602.

What would be the best (i.e. most effective and inexpensive) way of
boosting the signal? A high gain omni-directional antenna, or a signal
booster/repeater?... Antennae seem reasonably easy to get hold of, but
vanilla boosters seem few and far between (I see Netgear make a few,
but not for the UK market).

Can anyone shed some light?

Thanks,
Christopher Harrison