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#11
There is a workaround that might allow you to in-place Upgrade HP to Enterprise, but it is not advisable since Enterprise uses volume licensing which is completely different activation method than HP.
So I would do a clean install, which means you can use the install DVD's Custom>Drive Options tools to delete both the 199mb partition and C:, then create a New partition there, Format and install. Back up your files first.
If you decide to keep HP on C and still want to merge the 199mb SysActive Boot partition into it, we can give you the steps to recover the disk space and MBR into C using Partition Wizard CD and Win7 DVD or Repair CD.