i have mandrake over xp, and i am kind of newbie as well. i did some tests before installing on my laptop, i used my old system for punchingbag.
after those trials, my conclusion is that, the best way is resizing your xp partition for space for linux before install ( assuming you first have installed xp), or installing xp on partitioned harddrive. When you have totally empty partition even not a formatted one for linux, mandrake will let you choose to install on that partition no problem. i found it easier to use bootit or other partition managers to create partition space for mandrake. Because mandrake`s partition manager gets confusing for a newbie.
i used bootit for partitioning
thou i would say you can try getting imaging of harddrive just incase. if you understasnd partition part , most likely you wont mess up
for me hardest issue was understanding,
/
/home
/swap
you can try having / and /home partition around same size. also remember mandrake needs to format those new partitions due to filesystem
partitions mandrake creates, which are standart linux partitioning as far as i know. and mandrake`s partition amanager does not lead you simply, but i think there was an auto way in mandrake, and that works nice and simple when you have the partition ready for before mandrake install as i mentioned
my worst problem was after installing on my laptop, at some point i did upgrades through mandrake, and i did not have enough space either on my / or /home
mandrake would not start because could not create temp files during boot. that was a mess, it was easier to reinstall than solving the problem
thou try having at least 8 gb for linux at least, unless you know you wont install new stuff frerquently
in general installing mandrake was faster and easier than xp, i cannot talk about other distros but i was fairly happy with mandrake for first choice
i hope this helps you little