I have the same laptop and put a Crucial M4 in there. It was not hard to do at all, there is a small hatch cover on the left hand side which you unscrew from the bottom. The hard drive slides right out.
Switching to SSD has allowed me to keep the laptop for at least another year or so. It made things "zippier" but not exceedingly so. I think the sata channel is the limiting factor, but I don't no for sure. I put an SSD in my desktop as an OS drive, and it blew the pants off the thing. It's like having a completely new computer, and it's vintage 2009. I was a little disappointed in the speed increase on my E6500 though. I plan on futzing around with the settings to see if there's anything I can do about the speed.
@Cmontagu: Thanks for the reply. It's been a long time and I completely forgot about this question.
Finally I bought a OCZ 120Gb, so now I can give my 2-cents: I can't compare with a SSD on a desktop computer, but the speed boost was fantastic on my E6500, apps start really fast (GNU/Linux) and the overall responsiveness is great. Money well spent. I had a problem, though, the SSD stopped worked after a year (and I lost some data), fortunately it had warranty . So the moral of the story is: 1) SSD are great, 2) make backups.