How to Add 2nd Drive - newbie

Sorry for this 'simple' question - new to mac and have a concern. I have two pc's, one mini mac and the other winxp that are both hard wired to the same router to share the internet connection. Both pc's have a requirement to back up things like photos etc. I think a simple way of doing this is to put a 2nd HD (it will go in the windows PC as it is a tower case) and have two partitions - one NTFS for the winxp machine and one Mac OS Extended Journaled (is that the right one?) for the mac mini. Question is - will the mac mini recognise the new 2nd HD on the LAN or will I have to do anything to make it 'see the new drive'? I was looking at complete file sharing betwee the two PCs but I have just read about a Leopard bug that can wipe out user data when a guest account is set up and so far all the winxp/mac file sharing web pages I have looked at seems to want to create a guest account on the mac for file sharing. As this is not my mac (mother-in-laws) I have decided not to go down that route.

Hmmm..... this leopard bug is for Snow (10.6) so does not apply to me - the mini mac above is 10.5; sorry for that. Would still appreciate advice on easiest way to get mac to see 2nd HD on local lan.