The default Linux kernel of Debian Lenny is of course very stable - but a little outdated. If you're the more adventurous type (or just need support for newer devices) you might like the idea of installing a more recent vanilla kernel? Luckily, Debian makes this task quite easy and you'll end up with real Debian kernel deb-packages! I'll provide a small HOWTO here which you might follow and a small script which will automate everything. I gathered most of the information given here from the official Debian documentation (have a look at this and this).