Help with hard drive on sony vaio

I have a sony vaio laptop model pcg 7m1m, a couple of years ago while it was still under warrenty it started acting weird so i sent it back to sony and they said it needed a new harddrive which they replaced, got it back and everything has been fine for a couple of years. Now im having the same symptoms again, obviuosly lappy is now outa warranty, and i was wondering how hard it would be for me to replace it myself?
So my questions are
1. How can i tell 100% if it is the harddrive thats on its way out?
2. Where would i purchase a new hardrive?
3. Can a complete novice like myself fit it and get it working?

Also i think i would need to create a new boot cd before i remove old harddrive, is that still possible to do?

 

You wont need to create a new boot CD ... to test the HDD ... insert your original boot CD ... restart and boot from it ... assuming its XP, press r when asked ... then type chkdsk /r ... once its done, reboot the machine and remove your CD, when you desktop is loaded, right click on My Computer and select Manage, then select Event Viewer, then select Applications ..., if you sort your entries by date, find the latest one name winlogon ... down the bottom it will have a heap of information when selected, find where it says (x) KB Bad Sectors and post it