1st - Mostly likely you have corrupted the MBR, probably to the point of requiring you to reinstal Windws 7.
2nd Had you used he Windows 7 back up (located in windows 7 control panel) you would have been able to fix your Windows 7 quickly (about 15 minutes) by just inserting your windows 7 installaion disk (or the "repair disk that you would have been prompted for after the backup image was completed) and selecting repair, then restore from image.
3rd DO NOT recommend using windows 7 and xp off of the same HDD. You would have been better off removing the win7 HDD and instaling XP on a 2nd HDD. I know this requires swapping HDDs - I do it all the time.
4th I do not think that XP has the proper drivers for Your Netbook, so would require Using the "F6" option to input newer divers.
1) Boot to a linux disk and see if you can read your drive so that you can back up your data that yo generated - Windows and program files are toast.
If you did NOT heed the warning about creating a restore disk, then
2 Beg/barrow (DO NOT STEAL) a windows 7 installation disk and install windows 7. DO NOT enter the KEY when prompted. after installation enter YOUR key prior to activation.
3 Only ather alternative to #2 above is to go to Netbook Manuf and Purchase a restore disk.