Have backed up my old windows xp hard disk and wish to purchase a Mac. What troubles will I have with old info?

Remember to do your backup as a file copy and not using some proprietary backup solution. The copied files can be copied to the mac, where as some BU software on Windows uses encryption or proprietary file formats that may give you some problem.
Your MS office files can be moved over as well as an export of your Favorites in IE. With Firefox you can take everything over by copping your user profile I can no longer remember the path in XP.
Your applications will not move over. And data from email clients can be tricky to import especially Outlook but it is a snap from Thunderbird or Euduora into Mail or back into Thunderbird or Euduora on the Mac. The next office for Mac will include Outlook in the place of Entourage so that might provide a better migration route.
Openoffice.org offers a good alternative to MS Office for free and it will read and write MS Office file formats.
I believe you will enjoy your computing experience much more after the switch to Mac OS10.