Switching external hard drive from PC to Mac

Hi! I just just switched to mac and bought a LaCie external hard drive in order to save the stuff I wanted to keep from my VAIO. Now I want to keep that stuff on that hard drive and put stuff from my new MacBook pro onto it as well...can I do that? If so, how (please keep in mind I am not computer smart - at all)? If not, what's the alternative?
Thank you so much!!

As long as the LaCie is formatted to FAT-32 you can use it for both your Sony and the Mac. If the LaCie is formatted to NTFS you'll need third party driver support to be able to read and write from the Mac. Your Mac can read NTFS but not write to it.

Regards.