Never built a dual boot before (Debian/Vista) - any suggestions?

[Jesse]

I have to replace the laptop hard disk so I'm going to try my first dual
boot, of Linux + Windows.

Any recommendations on the procedure?

For Linux, I've used Ubuntu (10.7) and Centos (6.4), and I definitely do
NOT want Centos ever again as it is just too hard to find modern user
applications. All the talk of the latest Canonical spyware bothers me.

So, I think I'll try either Debian or Fedora, probably Debian, since
my key requirement is a typical set of desktop apps without spyware.

For Windows, I have Vista and WinXP installation disks which are not
on any other system, so I think I'll go with the slightly newer Vista.

The hard disk is a 500Mb drive, which, I'll partition, I guess,
arbitrarily at half for Linux and half for Windows (unless you have
a better idea).

My question?
Q: What are the unseen gotchas I should know about?


Note: Googling, I will likely try to follow one of these DIYs:
https://wiki.debian.org/WindowsDualBoot
http://forums.justlinux.com/showthread.php?148963-Installing-Debian-on-
Windows-XP-Machine-Hard-Drive-Partitioning