Now lets see
1) The home partition, some distros use this to store user settings, info in general and your documents. I say some distros cause some others don't (by default that is), such as Fedora Core 3. Advantages? Hrmmm... I don't know about that but I suppose it gives some security in case something goes awfully wrong with your linux root partition.
2) When reinstalling WinXP theres nothing you can do to prevent the bootloader from banishing (WinXP SHALL it your bootloader). Just remember to be careful when you reinstall the XPmonster, take care of the partitions, don't touch you linux partitions and you should be fine.
Now, as I said WinXP will eat your bootloader so you have to reinstall it, here are the steps:
a) Boot you computer with your Linux install disc (the first disc of your distro that is, or the only one
b) At prompt type:
c) After some screens you should come to a bash prompt (something with a $ on it maybe), there type:
d) Reboot (just type exit as many times as necesary for the system to reboot)
e) Once you reboot from your hard drive you should see the bootloader again
3) Im too a Linux
so I got my hands in a book called (simply) Linux 2nd edition by some Petersen bloke, it was outdated but I found it useful. As for websites there is no greater wealth of knowledge than LinuxQuestions so you are on the right track here.
Hope this helps.