Big Analytics Discrepancy

I use Google analytics and another web site analytics software that my web developer provides.

I compared the 2009 number of viewers. Google analytics = 51,000, other analytics software = 325,000. Any idea what I'm doing wrong?

Two big possibilities.
1. There is a data collection problem.
2. The difference is entirely in HOW the two packages decide that something is a unique visit or unique visitor.

First you should realize that no analytics package will be perfectly accurate. Get over that idea. Analytics is about trends. If you have 50k visitors in google this year and 70k next year that means something.
Secondly you need to read up on the documentation (assuming there is any) and see how each package tracks people, what each package means by a 'visit', a 'visitor', how many and how long it keeps history on individual visitors. etc.
Then you might try creating a sub-domain (ex. analitics.[domain-name].com) and hitting that sub-domain with fully known visits under controlled circumstances to experiment with the two packages.