I've heard from a few sources that the 70-270 exam can be used to meet the client requirement in MCITP: Enterprise Administrator. I wanted to know for sure, so I went to the source and emailed Microsoft Learning.
They sent a reply stating that 70-270 does not meet the client exam requirement for MCITP: Enterprise Administrator. You will need to sit one of the Vista exams or the Windows 7 exam. It's quite odd that it doesn't meet the requirement, as you could use your Windows 2000 client exam as a pre-requisite for MCSE on Server 2003.
Anyways, I intend to study the Windows 7 exam early next year.