When I do a search on "MA623LL/A" using Google, it seems to be an 8GB touch. Doing the same on "MB376LL/A" show it to be a 32GB touch.
There has only been one iPod touch line, in 8GB, 16GB, and 32GB capacities (so far). The 32GB model was added in Feb 2008. The 2.0 software was released after that, so the more recently sold had the 2.0 software pre-installed.
How do I tell?
If it's used, ask the seller. At worst, you'll have to pay $9.95 to download the 2.0 upgrade.