Dell has released a new BIOS for the XPS 410 and Dimension 9200, which they have marked as Urgent (in big bold and red-colored text). BIOS 2.5.2 corrects problems the system was having when in Gigabit Ethernet environments. It’s not clear if this also applies to systems with a 10/100 controller… or what else Dell didn’t note in the change list… so just go update.
Update: Dell has pulled the update. Judging from the comments below, the update was randomly frying Ethernet NICs on-board, though I cannot reproduce this on my system.