I understand your requirements to be:
1 - Buy a desktop not too expensive
2 - That performs well form family use (Internet, Office & Multimedia)
3 - That will allow you to continue using the software you have today on XP
Where is my advice:
Advice number 1: There are four variables that affect performance (CPU, HardDrive, RAM memory and Graphics Card). You can check their rankings on this Website (), what I did when I bought my last laptop was I weighted the several variables and come up with a combination that was balanced, but it took me three months to choose, so I am not sure if that is a good practice
Advice number 2: Choose a vendor based on their technical support ability and warranty offers. The location of the nearest support center or shop, as well as their reputaion, is also important.
Advice number 3: Your computer will keep you satisfied for a limited amount of time (3-4 years), take that in mind.
Advice number 5: Don't worrie too much about models and technical details, it will drive you crazy, but understand enough to be able to chose wisely.
Advice number 6: Office 2000 is no longer supported by Microsoft, since July 2009, so ponder replacing it by Office 2010, Open Office or even Google Docs.