Sharing files between Windows XP and Windows 7

XP cannot join a homegroup
you need to change the name and use a workgroup

have a read here
Share Files and Printers between Windows 7 and XP
http://www.howtogeek.com/howto/windo...dows-7-and-xp/

Here’s how you can get your Windows 7 PC to share printers and files with XP and Vista PCs--and even a Mac
http://www.pcworld.com/article/18423...7_edition.html
http://www.howtogeek.com/howto/12246...-to-windows-7/


Tips for Troubleshooting Windows File and Printer Sharing
http://compnetworking.about.com/od/w...ilesharing.htm