Hi Mark. Just tried it on windows XP, worked first time. with a generic usb lead one.
QUESTION 1 what windows are you using.?
2. what version of poi loader I used 2.7.0 from here
http://www8.garmin.com/support/download_details.jsp?id=927).
3.
what garmin mine is Nuvi 250.
4. Try this first plug in garmin to computer first, wait about 30 seconds, then run poi loader, you should see where to save poi to, select the first option then click next. on the next screen you should see a tab called find Device, click this your device should show up.
p.s. if it works be careful on the third screen the option you select here will overwrite the poi's all ready on your unit.
let us know how you get on.