My entire mac partition disappeared

Sorry, this may tiek some time to read. But I really need some help with this.

So I had a windows vista partition my mac (which I have done before) And i guess my key ran out or something. So a friend of mine gave me a Windows 7 disc. I couldn't get it to just boot from disc, so i logged onto my mac partition and tried to delete the windows partitions (also something I have done before). Like usual it gave me a hard time.
Eventually I got the 45 gigs thats I assigned to windows to erase all data. I then decided to restart my computer with alt held so I could chose the empty partition and boot from cd there. To my surprise I found that I can no longer chose 'MAC OS X'
This doesnt make sense because I didn't touch the mac partition. I didnt format to single partition. I payed special attention to not messing with any of the mac data. So with no options i loaded the empty 45 gig partition and was able to book windows 7. When the setup asked what partition to chose for windows 7 I saw that my once mac partition is now an unnamed partition that has nearly as much free space as overall capacity.
I am currently installing windows 7 on my 45 gig partition so I have something to use. But what are my options now? Is it possible to restore my mac setting? and If not, how do i go about potting Mac OSX back on my computer?
Thanks you very much in advanced, and I really hope this doesnt happen to anyone else. Its starting to seem like I will lose everything I had on my comp

You've erased your mac partition.
Your options are to install from your install disc/discs, or restore from your backup (assuming you have either or both, which you should)!
Are you running OS X 10.5 or later?
If so, you should follow this guide.
Using Boot Camp to install Windows 7 on your Mac: The Complete Walkthrough – Simple Help

Without a backup, and/or install discs you should never mess with partitions, or make any major changes to your system.
Without install discs, a bootable backup is essential!
Backups are essential regardless as a safe guard even if you have install discs, as if the hard drive dies, you can pretty much say goodbye to everything on it.
Moral of the story is, I hope you have a back up.

Thanks for the info. But unfortunately I do not have a backup. But i do have the statup discs. I not have everything set up again, but my old data is all gone. I'll have to deal with it though. I plan to buy an external and make a backup on it asap.
Again, thanks for the reply.