I have a similar problem (with the return key on the LHS). The problem is likely caused by dust getting under the keys. I used to have the same problem with the toggle - found sticking the end of a paperclip under it and wiggling it about fixed that a couple of times. Not really possible for the non-toggle buttons though
This site tells you how to dismantle your phone:
http://www.formymobile.co.uk/Dismantle/k800disassembly.htm
I don't have the tools though and my speaker's bust too so think I'm going to have to just get a new one (18 months old so not too bad I guess..)
Mark
May 2008