There is a forum post over on Xbox Core where the forum poster claims to have got his hands on a test version of the 360.

my step dad works here in seattle for xbox hes the forgein tester guy. He had a trip to mexico to test the new xbox so he had to bring it home and he let me play it. There arnt any xbox360 games yet i guess so all i got to play was halo 2. but all the test stuff was on there like dolphin and light shadow stuff, Oh and the XBOX dashboard . I uesto hATE xbox purley a PS fan. but WOW new xbox has some COol stuff. First i tried dolphin witch doesnt have liek GOOD grapics or anything its just a frame test and the xbox was geting 3000+ frames witch was pretty stuinning for me. and the Xbox dashboard is amazing im not aloud to tell everything about it but WOW theres soo much crap on the xbox and some of it is sooO miscelanius. theres xbox arcade were u can Dl like arcade games and crap and u can stream music from ur PC to ur xbox and tons and tons and tons of other crap.

Well worth a read even if it does include a dodgy haircut and awful spelling.