Originally Posted by davepi
It's my first time playing with partition tables so I don't know too much.
That's a scary thought.
Make sure you have good backups - of everything.
There is a utility similar to fdisk for GPT - called gdisk. Homepage is here
Read all the doco - a relevant quote
Do not attempt to convert a Windows boot disk from MBR to GPT form unless you're an expert!
(the authors emphasis, not mine).