[H] annoying W7 home network

[Winterlight]

I had a couple of PCs with Win7 PRO set up to share with advanced 
settings = normal type shares. Then I added a third Windows 7 PC when 
I upgraded my IBM tablet to Win 7 Pro and was having problems getting 
it to share its files... so I setup the windows 7 home network on all 
three  Win 7 PCs and all windows 7 PCs share everything .

But now my XP boxes can't connect to the windows 7 shares, but the 7 
boxes can connect to the old XP boxes as they always did., What 
happened and why does MS make everything so freaking hard when they 
attempt to "simply"  things.

thanks