E.g. Dell Singapore lists [link|http://www1.ap.dell.com/content/topics/topic.aspx/ap/topics/microsite/en/redhat?c=sg&l=en&s=bsd|this] PowerEdge 1950 with RHEL installed. If you search for Linux at Dell.com you'll see a [link|http://www.dell.com/content/products/productdetails.aspx/precn_390?c=us&l=en&s=bsd&cs=04|Precision 390 Workstation] box with RHEL available, but if you go to Customize it, there doesn't seem to be any way to get anything other than Windows.
It looks to me that one must have the patience of Job to get a consumer box with Linux from Dell.
FWIW.
Cheers,
Scott.