I posted my products on Froogle and they came and went rather quickly even though they had a 30 day expiry. The guys at Google recommended loading up the file each week to keep the products in Froogle. They didn't show my products for a short while as I had Free P&P listed which is not allowed, however more than 3,000,000 products have Free P&P listed in the US Froogle and they don't get their products dropped like I did, I thought that was quite odd!?
For the best instructions on creating and uploading your file look at Google Base, just type Google Base in Google and it should come up...
Cheers, Trevor
www dot gaycardshop dot com