Are you sure you're not a little confused on SharePoint's hierarchy terminology? Based on the URLs you're showing for those sites (/sites/HR and /sites/IS), it looks to me like they're already full site collections and not subsites... (I'm saying this b/c
the "/sites" component of their path is likely to be a wildcard managed path, under which site collections are placed). As I look at your info, it looks to me like intranet.contoso.com is the top-level web application's URL (with a site collection at that
top-level URL) and IS and HR are site collections beneath it at the "sites" wildcard managed path.
If that's the case, you just need to create a new content database for that web application and move one of the site collections into that content database (this article has good info on how to do that:
http://technet.microsoft.com/en-us/library/cc825328.aspx)
If your URL info above isn't correct, or if I'm misreading and you're sure that HR and IS are subsites (also known as "webs" in the SharePoint object model), then its going to be much more difficult, because its not very easy to promote a web to a top-level
site collection. You may be able to try the Export-SPWeb CMDLET to export the web and import it to a new top-level web within a site collection, but I suspect that won't work very well if those webs are as large as you say they are. You may have to
look at a third-party migration tool to see if one of them can be used to promote that much content from a web to a site collection.
But, based on the info you've got above, it really looks like you're talking about HR and IS as site collections, in which case it shouldn't be too bad to move one into a new content database.
John
MCITP and MCTS: SharePoint, Virtualization, Project Server 2007
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The SharePoint 2010 Disaster Recovery Guide and
The SharePoint 2007 Disaster Recovery Guide.
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