New build, old Windows?

I'm currently ordering all the parts to rebuild my PC from the ground up. But I'd like to keep my old hard drives/SSD, and most importantly, keep my old Windows installation. I've been buying upgrades since XP, and I'd rather not buy a whole new version of 7 or 8 (especially since I'm a student and I got the upgrade versions for free).

So, if I simply take my old system drive and plug it into the new mobo, will I be able to download all the new drivers etc, or will I be completely screwed? And will my license transfer? I'm pretty sure the student license can be installed on 2 PCs with the same key.

For reference, here's my old and new setups:

OLD
Mobo: ASUS A8M2N-LA (Micro ATX AM2 board from an old HP pavilion)
CPU: Athlon 64 X2 6000+ (3.0 GHz)
4GB DDR2
XFX Radeon HD6850
LB Blu-Ray reader
System drive: 120 GB SSD
Data drive: 1TB HDD
Backups: 1.5TB external USB HDD/ 1.5 internal HDD combined into single Storage Space
Windows 8 Pro

NEW
Mobo: ASUS P8Z77-M Pro
CPU: Intel i5-3570K
16GB Kingston HyperX Blu
XFX Radeon HD6850

Same drives, and hopefully the same Windows!