What Intel allow you to do with some chipsets is use part of an SSD to cache a hard drive. You get something similar in performance to the Seagate Momentus XT Hybrid. I have two SSDs in my desktop, one for OS/Apps/Games and a second for games and cache for my 1TB hard drive. Over time it learns what you use and stores those files in the cache allowing quicker access.
The diagram on this page shows how it works:
If it were me I would do what Dolleeh suggests but I would get a 180GB SSD and then a 7,200rpm hard drive and use SRT to speed up access. Not sure but PCS might be able to configure the build of Windows to use SRT.