Can I install original copy of Windows (OEM) on more than one partition on the same computer?

As stated in the XP Pro EULA

Installation and use. You may install, use, access, display and run one copy of the Product on a single computer,
such as a workstation, terminal or other device (“Workstation Computer”). The Product may not be used by
more than two (2) processors at any one time on any single Workstation Computer. You may permit a maximum
of ten (10) computers or other electronic devices (each a “Device”) to connect to the Workstation Computer to
utilize the services of the Product solely for File and Print services, Internet Information Services, and remote
access (including connection sharing and telephony services). The ten connection maximum includes any indirect
connections made through “multiplexing” or other software or hardware which pools or aggregates connections.
Except as otherwise permitted by the NetMeeting, Remote Assistance, and Remote Desktop features described
below, you may not use the Product to permit any Device to use, access, display or run other executable software
residing on the Workstation Computer, nor may you permit any Device to use, access, display, or run the Product
or Product’s user interface, unless the Device has a separate license for the Product.

Because MS produces a computer ID My Computer - Properties based on the licensing Key and hardware profile (mostly the motherboard) that is unique to each "computer" and relays that information to MS servers, all three partitions will have the same hardware ID, and cannot be used concurrently, there shouldn't be any restrictions per the EULA

Yes, as long as only one install is being used on one machine at any time. Here's the EULA: Windows XP EULA In the section about storing images of XP on a network, it says you need to have one license for each separate workstation the product is run on. So if you are only running one copy at a time on the same machine, and you are not transferring it, I read that as the same machine.