I actually asked this same question to a sams club computer/electronics department manager just today. He said that he was in the dark about it, he had asked a few days ago and was told that they were holding off bringing in any more laptops or PC's until they (Sam's) were guaranteed to get the Vista preinstalled ones.
He went further to say that the selection of the lappys they had was pretty old (by relative terms, in that they had not gotten a new model in about a month) and he was hoping they clearance them out this coming week and get the new ones in for the week of the 30th. He did know that most would come with Home Premium or Business, to replace the MCE and XP Pro levels, but that matchup is pretty easy to figure out.
I asked also about the Vista upgrades (boxes), he said sku's were allocated and they would have them out on the 30th, price he had not checked but maybe 'a little bit' under what Walmart would have them for, which he said he was told by his higher up to be simply MSRP at this time. But like he said anything and everything is subject to change..
This guy has been there about 7 years in that capacity so I'm pretty sure he's not talking out his azz. He's a good one to talk to now and then about stuff, pretty knowledgeable overall. Quick to say "I'm not for sure or I don't know", rather than make stuff up like some.