There are some good tips on harness training kitties on the following website:
Catnips.

Personally, I prefer
Lupine Harnesses that clip shut as they're easier to fasten (my kitten prefers them too, as she doesn't have to wait for it to be buckled up LOL). Lupine ones have to be ordered from the US, but are still fairly cheap, and are well worth it. The lead I use is a FlexiLead, and I last saw these cheap at Asda. My kitty took to a harness very easily, and she enjoys her walks very much. Let me know if you'd like any more help.