If your Mac originally came with Tiger, then I think a clean install might break the iLife things that came with your Mac. (You cannot easily install those on a clean installation of a newer OS X, I think, but I might be wrong. Installing iLife that came with 10.5 seems fine though, but your mileage may vary.)
Apart from that it's totally fine (and legal, if you own both Leopard and Snow Leopard for that Mac).
However, the "Erase and Install" option is no longer part of the normal installation, so you'll need to use Disk Utility (and backup your personal files). See as many as 44 steps at Apple's Mac OS X v10.6 Snow Leopard: How to Erase and Install.
As a side note: "Archive and Install" is no longer available at all. But apparently: if you need to reinstall 10.6, it automatically archives and installs for you (or, one can do it manually).
There is a thread that discusses using IsoBuster to create an image. You need to back up the entire hybrid disk (at least for 10.6).
Can you access another Mac to do this? If so, in Disk Utility select the drive (not the volume) and click the New Image button on the toolbar to save a DMG as a DVD/CD Master. Funny idea: go to an Apple Store with an 8 GB or higher USB stick, buy Snow Leopard, then use one of the computers there to create the DMG.
Once you have the DMG, rather than using diskutil at the command line, just use Disk Utility and create a 10 GB partition at the end of your drive (under the Partition tab for your drive). Then go to the restore tab and select the DMG for the source and the new partition for the destination. Make sure Erase destination is checked and double-check that you're dealing with the right partition.
Note that I'm using Disk Utility on 10.6 and I haven't worked with 10.4 in a long while. My thinking is that Disk Utility hasn't changed very much and I hope that the features that I'm talking about exist and behave as I would expect on 10.4.
Finally to install Snow Leopard, reboot your computer, hold down the ⌥ key as soon as it starts up (chime) and you should be presented with two options, both with a hard drive icon. The second option should say Mac OS X Install DVD. Select that.
EDIT
Specific IsoBuster instructions from the above thread:
Open IsoBuster -> right click "DVD" on the left side -> choose "extract dvd " -> User Data (*.tao, *.iso)
Name the file whatever you want (ie "Leopard") on the "Save as type" choose ".iso"
Click Save and wait for image to be created. After it is finished it will probably ask you to save a ".cue" file as well...go ahead and save it, but you should not need it.
Best Answer
Most of the install DVDs that Apple ships with Macs are model-specific, because they often contain bundled software and Apple doesn't want you installing that software on Macs that didn't come with it. If you can find another DVD for the same model (and by "model", I don't mean "MacBook", I mean something like "MacBook2.1"), you're in business. Otherwise, you need to find a generic install DVD (i.e. one sold separately from any particular Mac) for a version o OS X newer than what your model originally shipped with. For instance, if your particular model originally shipped with OS X 10.6.3, it probably requires a special build of 10.6.3 with drivers for its new hardware added; a generic 10.6.3 (or earlier) DVD won't have these, and won't work; a generic 10.6.4 (or later) DVD should have the drivers and work properly.
Now, there may be a way around this if your MacBook has FireWire and you have a buddy with another FireWire Mac (and an install DVD for that Mac). What you do is start your MacBook in target disk mode (hold the T key as it powers on, and it'll pretend to be an external FW hard drive), connect it to your buddy's Mac via FW, then bood your buddy's Mac from the install DVD and use it to install onto your Mac's hard drive. Then, with your MacBook still in target mode, reboot your buddy's Mac (from your HD again) and update to a newer OS version than your MacBook requires. At this point you should have the drivers you need, and can shut everything down and restart normally.