Time Machine without Airport? I'm a very new Mac user. I just bought a MacBook Pro and I'd like to use the Time Machine backup. Unfortunately, it seems like I can only keep my laptop mobile by using an Airport router. I was hoping that I could backup to a HDD shared by my Window 7 desktop.

Is this pie in the sky? Is there a backup alternative that I could use that would give me the functionality I'm looking for?

Additional Information

I'm not looking to back up files per se. My documents, pictures, etc, are backed up on mirrored externals on my PC. I'm looking for a backup that will allow me to restore my applications and their settings should the Mac ever crash - installing and configuring a system is the most time consuming part of rebuilding a machine.
Time machine requires a specially formatted hard drive - it doesn't have to be an Apple drive and indeed can be anything you can connect to the machine, but it must be HFS+ and as such cannot be shared by Windows (FAT/NTFS). 

My choice in this situation (I too have a W7 machine too) was to purchase a relatively cheap Western Digital Portable HDD from Amazon, let my Mac format that and use it exclusively for backups. I couldn't find anything to share them between machines at all. 

If you're only looking to backup files, however, Dropbox may suit you well. It's free plan provides you with a 2gb folder that syncs between your computers (and the cloud). 

I'm interested in what you said about an Airport router - your Macbook should be able to connect to any Wifi A/B/G network (so pretty much anything, for instance the free router your internet supplier provides).