Most distros should be able to resize your partition during install, just make sure you have your data backed up. You could create these partitions in advance through Partition Magic similar and then just point your Linux installer to them.
The L10 is quite Linux-friendly, check my signature for running Gentoo on it, and the only problem I had was with the power management as it needs patching separately (follow the link in my instuctions). Pretty much any distro should work fine, as the graphics, sound + wired network card are fairly common and shouldn't cause problems, and the wireless card is well supported and very easy to configure with ndiswrapper.
Not sure of any Slackwares-specific instructions, but it's fairly common hardware as detailed before, so it shouldn't be too difficult to put Slack on it if that's what you're comfortable with. Since it's a fairly nippy laptop, SuSE should also happily run on it if you liked the eye candy it provides!
But I'd say stick Linux on it rather than leaving it solely for Windows
