Hi Diane, I think I can help you out here as I've had a chance to use almost everything out for PC. In my opinion, for the price you're thinking of, I would definately get Cakewalk 8 or 9, either wavelab or soundforge, and some plug ins. Waves, DSP-FX, and the sonic foundry stuff are probably the best, though Cakewalk has some nice ones too.
Cakewalk is far and away the best of the midi set-ups. Cubase has a stupid interface, very poor documentation, and is an absolute PAIN IN THE ASS to sync. It took me several hours to not manage to get my external hard disk recorder to sync up via SMPTE on cubase, and 10 minutes on Cakewalk without looking at the manual. The general concensus seems to be that the timing is better on Cakewalk as well, an issue when you're pushing the limits of your machine, which you will do. Almost everyone I know who has used the lot prefers to write on Cakewalk. Some take the tracks into Logic Audio after that, but a lot of guys just know they can work faster in Cakewalk. Logic Audio is very powerful, but has the WORST on-line documentation, practically useless. If you're just making your initial forray into PC recording, it is guaranteed to give you more headaches, and you won't be taking advantage of its extra features anyway. Samplitude is pretty nice, but doesn't have the same support as the others. All the others have a lot of really cool add-ons. (Excellent score writing and orchestration untils for Cakewalk). Sometimes you can also pick up used copies from people who have switched platforms, and then pay for the upgrades.
My biggest beef with Steinberg is that they make things look really cool, at the expense of ease of use and getting as much info on the screen. I can set up Cakewalk so that I get a minimum of clutter and maximum information on the screen. I don't want to watch the flying faders, I want to write music! Currently I use Cakewalk for almost all my writing and recording, Logic Audio when needed, and Wavelab and a variety of plug-ins for processing. How fast your machine runs also will affect your choice. If you don't have a flying set-up (Fast drive and chip) then you can't take advantage of the better real time support in Cubase or Logic Audio anyway. Cakewalk is definately the best when running on an under powered computer.
Oh yeah, the coolest plug ins in the world are sonic foundry's accoustic mirror, and Native Generator. Accoustic mirror will make you never touch another reverb until you can buy one for $10 000, and Native Generator is a damn powerful soft-ware synth and modulor processing tool.
Any questions, please feel free to E-mail me.
Iain.