Need to join VDMK files from separate partitions into 1 VM

I'd go with expanding the C: and copying the data from the D: across. ELse the commandline tool vmware-vdiskmanager.exe

http://www.mahmoudthoughts.com/2009/07/merge-2gb-vmdk-files-to-one-single-vmdk.html

afaik this is not possible with vmware-vdiskmanager - so you would need to do that with vmware converter standalone (free)

//edit: oh yes, didn't think of simply extending  the c-drive :-)
that would be the easier and faster solution

As per my understanding, You want to mount 2 VMware vmdk files in physical machine. If it is correct then please perform below steps for same.

1. VMware provides a tool called “vmware-mount” to mount VMDK file in physical system as a separate hard disk drive. Download it from below website.

https://my.vmware.com/web/vmware/details?downloadGroup=Disk%20Mount%20Utility%205.5%20Driver%20Tools&productId=46

2. Install the tool in your physical system, once you finish the download.
3. By default, the program will installed into “C:\Program Files\VMware\VMware DiskMount Utility”.
4. Open command prompt and go to the installation location by

cd \“Program Files\VMware\VMware DiskMount Utility”

5. Suppose we have a vmdk file located in “C:\Windows XP Professional.vmdk” and we need to mount that in our Windows operating system. as a K drive. Then need to execute below command for same.

vmware-mount K: "c:\Windows XP Professional.vmdk"

6. Now the VMDK file will mount into our system as K drive.

This answer wasn't exactly what helped me.  The root problem was resolved by allowing VMware vCenter Converter to convert the OS drive in its full size.  I was chopping the drive down from 180GB to 110GB which was all that was used.  I selected not to do that in the converter and the transfer and conversion was successful.