Is there a standard way to benchmark a Windows VM performance from within the guest OS?

I tend to use the same products I use to benchmark physical hardware.

http://www.passmark.com/products/pt.htm

Skip the 3d test of course, but the others can be helpful, especially the disk and networking benchmarks. Make sure you are using the proper network & IO drivers, and make sure all your windows settings are optimized for VM.

For testing the networking, I use iperf and netperf to stress test that.

For testing disk I/O, use sqlio which is another industry standard tool. Run both random and sequential I/O testing with different block sizes.

For the CPU/RAM testing, I can't think of anything for Windows off the top of my head.