You won't be able to use more a 3TB drive as a boot drive but you should be able to use it for mass storage. 3TB drives are new and I'm pretty sure that two 2TB drives will be cheaper than one 3TB drive. A consideration, though, is the SATA ports on your motherboard. You've only got four ports and I would guess that one of them is for an optical drive. Various things use SATA connections so open up your computer and check how many available SATA ports you have (your current HDD will be in one of them). Below is a picture of what your motherboard will look like and the four black/yellow/blue/white ports in the bottom right are your SATA ports.
http://h10025.www1.hp.com/ewfrf-JAVA/Doc/images/c00757541.jpg
If you have at least two ports open (after removing your current hard drive) then you can use an SSD as your boot drive and an HDD as storage. If you have three open you can use an SSD as your boot drive and two 2TB drives for mass storage.
For either the 2TB or 3TB variety, I recommend the Hitachi Deskstar 7K3000 for your application. It's a 7200RPM drive for high performance and they're slightly more energy efficient than the other drives.
As for an SSD, it's hard to recommend until you give us a size. Intel makes quality SSDs and I like my OCZ (although OCZ doesn't have the best reputation I guess). One thing, though, is that all your SATA ports are 3gb/s (SATA II) so don't wast extra money on a SATA III drive because you won't see any extra performance. Also, SSDs are one area where you don't want to get the super bargain basement models. Sometimes manufacturers try to have a fire sale on older drives with buggy controllers or drives that are asynchronous and you want to stay away from those.