How can we diagnose this problem? How to print a document from Win Xp if a printer is attached with win 7 in a network?

By sharing the printer from windows7 and add the post script drivers in the server which is Windows7 and connect to the printer from windows XP 

A Network connection by adding a printer on devices and printers then look for the IP Address of the printer after you add and installed it on XP you can print as long a you can....

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This link show you the steps from A to Z , How To Geek

By Sharing,........... the Printing can be done from XP To Windows7

Check first network connection where all of the computer with coneect into that network whether u want to print.then goto printer section wherther the printer is on or not.then goto print page.now test the printy page to apply into print from file.but be careful when their connected or not check how many printer are connect with network.when select a offline printer then print will not be ok.so printer selction is also required.If all of this is not ok go to Device manager from properties of My computer at Desktop on XP.then see ur printer name.click on right see properties,troubleshooting.from then any signal occured or not.then go to check fro trobleshootong On Help & suppourt. portion of XP.Their must be solution.