Windows XP rewrote my Mac.

Question

Hi,
I posted this under intel iMac but it was suggested I come here for help. I've pieced together all the info from that post.
My sister was using my computer and wanted to use Windows XP Professional Service Pack 2 in VMWare so booted a CD of Windows on my machine. There was a part that said you could put XP on the partition available so when she hit Enter it said that it couldn't be done but that she could go back and delete that partition and then reinstall it there. So she did that and then installed Windows on there.
Now everytime I turn my Mac on I get Windows XP. How do I get back to my Mac system?
I tried turning the Mac on and then holding down the option key as it started up but the only thing I get is an icon with the hard drive and the word Windows below it and an up arrow which I push and then it takes me right back to WindowsXP.
Right now I'm thinking my only option is to reboot from my original OSX install disk and don't think Keep User Preserved Setting will work because it's all been erased by Windows right? I know if you unplug and plug your Mac back in you get a file in the trash that says Recovered files and I haven't unplugged it at all.
I went to the C:/ drive and with my mouse hovered over it is says free space is 146 GB and Total size is 149GB and my intel Mac was 160GB large. Also tried sticking in my OSX install disk and hitting C after start up thinking I could try the save User preserved settings but I saw the hard drive icon and then a yellow triangle sign with a question mark that said I would have to hit Options to delete stuff and I hit that to see the buttons and it said erase, cancel and something else. It said it would fresh install stuff. I ejected the CD out right away and didn't go any further.
Is this fixable to get it back to the way it was or have I lost everything? If so if I brought it in to a Mac technician could they bring my files back?
What about using Prosoft Data Recovery X? I don't have an external hard drive but could get one and I am using my sister's Powerbook PC at the moment.
S.

Answer 1

rebotfc,
No, but I'm running File Salvage which is showing thousands of files right now but I only got 4 GB of space on my sister's computer to save it to. I have no idea how it will save stuff or how it will all look. What gave me hope was I read something in File Salvage manual that said most people overwrite using the NTFS quick mode and that is what happened here so I thought it was worth a try.
Now two things I'm thinking about here. I could stop the scan and wait until my hard drive gets here from Apple (just placed my order on the G-Tech 500GB Quadra Drive) which may be more than a week (that's fine I've got my sister's computer to use).
The other option is I do have a bootable Disk Warrior as well that I could stick in my computer and boot up from but will it cause more damage if I do so? Thinking of waiting it out stopping the scan and rescanning when I have my external drive. There are things I can delete off my sister's computer but no where near 160 GB worth. I don't want to do anything to lose what File Salvage is finding. I'll try Data Rescue II again later but happy files are being found right now.
I've heard something about file hierarchy and have no idea how this will configure files. (Does it just mean files won't be in the right spot and you have to configure them yourself?)
It is okay to stop the scan and rescan later on right? Nothing happens to the files?
S.