Heh lemme reitterate something...
LEARN LINUX BEFORE TRYING LFS(Linux from Scratch
Otherwise you would be a true masochist.
Now on to your questions...
The only thing you should be able to screw up if you use common sense is your boot process, and that can be repaired by replacing the MBR. In other words have your windows installation disk handy if you need it quick, put it in and one of the options along the line will be to repair the MBR I believe(Find it before you begin just so you know where it is) That is your last ditch repair the easy way thing to get XP back.
Other than that a few suggestions... Backup everything in XP first(This step alone MAY screw something up), , defrag your HD(Very important for making the rest of this go smoothly)make sure you have plenty of room on your HD, and then resize the partition using a partition manager(NOT FDISK! It cant resize it can only delete erase and create) to allow for room for a linux distro, 10-20 gigs should be all you need depending on exactly how much you want to play with it. Once that is done, DONT screw with that partition for any reason and you should be fine(Will most likely be either hda1 or sda1, make sure you know which it is before continuing so you know what not to screw with)
Most of the time that step will go fine with a common distro these days and you wont have a problem. The only thing is you might want to make sure you dont stop the install from here on midway, just to be sure the boot manager gets loaded, this will allow you to boot into either OS. Again most of the time it wont be a big deal anyways though.
Once the above step is done and your partitions are set up, you really shouldnt ever have to worry about it again, at least as far as your XP partition, you may find you want to play with your linux partitions a bit but done correctly(Dont screw with your XP partition) there isnt much danger to your XP partition at all.
In as far as order, I would install XP first and Linux second. MS doesnt play well with others and XP overwrites the MBR(And your bootloader) so if you installed it second you would have to do a trick or three to be able to boot into linux again.
My personal advice for you though in as far as distros go, if being able to do LFS is your goal, start with Ubuntu(Preference will vary here depending on who you ask, I just tend to like Ubuntu myself), then go to Gentoo(VERY good learning distro once you get basic knowledge of linux out of the way, and an exellent stepping stone to LFS as it does a lot of the same things, just automates certain aspects at the way begining mostly and some of the compilation) then go to LFS, and stab yourself in the eyes.... Ok maybe not that last part but after all that is done I would bet at the very least you step back down to gentoo or a different distro.
In as far as programming goes... Heh learn to love Emacs(Some will tell you Vi, I love Emacs for it myself) and virtual consoles. Also look into learning CLI debuggers like gdb. You can use GUIs but once I got used to the CLI and Emacs I never looked back myself, though I dont program nearly to the extent you will.
However a side question for you. What laptop are you running? Mainly what are the main points about it as some things may not yet be supported in Linux, your best bet to tell would be to try to find it on tuxmobil.com and see what people note as not working, quite often youll find guides to get things that may have been troublesome working on there as well to help you get started.
After all that done, my last reccomendation, learn Audio and start helping projects like ReZound
Ok shameless plug to try to get him more developers there
Have fun above all though.