Help Figuring Out Part Numbers for 8400m gs and 8600m gt

I'm looking to upgrade the video card for my Vostro 1500 from the 128mb 8400m gs to a 256mb 8600m gt. I was browsing around looking for the 8600m gt part number and I came to the conclusion that 'UW390' is what I was looking for. I did a search on ebay for 'uw390' and came up with a few listings. I made a few offers for one listing and they were all rejected automatically. Then made a higher offer at a second listing and had that offer accepted today. Went ahead and paid and didn't notice until a little bit after that the description of the item that I paid for actually said ' 8400m 256MB VIDEO CARD 'UW390'. Yes, I'm that stupid. That said, I've already gotten in touch with the seller and he said he'd be able to take a closer look at the item when he got back to his 'office' on Tuesday.

I'm sure I can work this out somehow and am not panicking, but I cannot for the love of god figure out what the actual part numbers for these video cards are. I'm seeing mixed results everywhere. Some places say the 8600's part number is 'UW390' while some say it's 'YY634'. I've seen both part numbers used for the 8400 as well.

Can anyone shed some definitive light on this situation?

Here's the item I paid for -- link

 

What are the chances that Dell started selling the 8600M GT as a 256MB 8400M GS? Both with 'uw390' as a part number?

 

UPDATE...

Opened up the lappy tonight and took a look at the card. Found 'YY634' on it, so a card with 'UW390' would have to be the 8600gt, no?