I'm thinking about getting a factory cd/cassette radio off of ebay. Will one from a 03-05 Silverado work in a 2000?

no.... only ones from 99-02 will work in your 2000

Ok, thanks. I'm assuming the 03-05 radios are double din?

yes and the 03 up has different connectors

Doesn't the '03 and up have the RDS and computer issue where it will not communicate with older units?

Be carefull cause you might need to have the radio unlocked by GM

yes the 03's and up communicate with the bcm and are programmed with the vin number ... but the rds has nothing to do with if it will work or not ... Radio Data Service or RDS is just a thing in the radio that tells you what the station call letters and slogan are if the station is set up to do that ... which most of them are not ... 02's and down just have a pin number that the owner programs in case of a theft