Right, first the disk - see if you just right-click the "unallocated" space, I think you'll get an option to create volume or something like that. you should just have to choose the size (I think it'll default to the rest of the space), choose the file system (NTFS) and click ok, then it should create and format it.you'll end up with an F: drive with the rest of the space. If you want it set as D: , then before you create the volume, right click your spinpoint, and change it's drive letter to F:. All the drive letters except C: are reasonably easy to change after anyway.
As for the benchmarking, I'm not so good at those type of things. But it does seem to be working, you're getting an increase in the 4K speeds, which is where it matters for system responsiveness I think. Do you notice your system being "snappier" since you turned on caching? Also, as it's set for a cache, it'll A) take time to figure out what files you use frequently, and store them on the SSD, and B) look not so good in benchmarks, as they'll write their own random data, rather than read/write your cached files, so the benchmark will seem lower than your actual performance, as benchmarks will have less cache "hits", and you'll see more the HDD performance from a benchmark test. The only way you'd see the SSD benchmark speed is if it was removed from the cache, and set as a drive in it's own right.
I think you'll notice the speed increase with the cache though, and it'll take a few weeks of your usage pattern to build it up, and show the benefit anyway.
You maybe want to bump a PM off to Sean Webster ( http://www.overclock.net/u/151997/sean-webster
), He's done some brilliant guides in SSD optimisation and stuff, and he seems to know storage inside out. I'll bet he'd be your man to give you solid advice on your storage setup. He'd be far better than me at advising you on tweaking your storage performance.