Trying to backup with time machine

I hooked up a 1 TB external HD to my Mac so I could backup my system using time machine. I have never done this before. The HD has some files on it that are a backup for my PC and I don't want to erase them. Time Machine asks me if I want to erase the files and I click NO. After that, the only option I have is to use Time Capsule.

My question is: "Is it possible to backup to a HD that already has some files on it or will Time Machine only backup to an empty HD?"

It is recommended (highly) that you dedicate a HD just for Time Machine. Do you have something else to put the PC files on in the mean time?

I have 2 Macs at home (MBP and MacMini) and each has a 1TB drive for Time Machine. The one for the MBP is hooked up to my Airport Extreme and it is only used for the MBP. For my MacMini, I have a 1TB drive hooked directly to it for Time Machine.

I too use a 320 GB HDD just for Time Machine. If you need to BU windows files, just get a thump drive or create two partitions on your HDD. One for TM and one for Windows. But DO NOT use the same partition for both.

Thank you for your comments. I had just assumed that my Mac would create a separate file for Time Machine. Sometimes the technology hasn't caught up to my vision!

Can you tell me if this is suboptimal?:

Bought an external 1 Tb "MyPassport Studio", which runs very fast for a 5400/8mb. Used for a 250 gb MBP, so plenty of room for backup.

I partitioned it with 60 gb for a bootable firewire service drive just in case or for certain utilities. And the rest is being used for Time Machine as well as some separate files. Seems to work just fine.

Is the trouble that other files going onto the same partition as Time Machine is harmful, or the drive being partitioned itself or both/other?

Thanks.

Genierose - You have to create the partitions first, or it takes the whole drive.

Stanley - Time Machine does a full backup, then when it backs up after that, it only does incremental (changed files, basically) backups. It saves them all until the drive is out of space, at which point, it starts deleting the oldest backups first and continues like that forever (theoretically). I would not suggest putting other files on the same partition as the Time Machine uses.