Maximum PC

I am planning on installing linux soon to dual boot with windows 7. I am running out of room on my current HDD though, so i thought before installing linux i would buy a new one and just install linux on that drive. What do you guys think of this plan? Should i buy a SSD since i won't really need much space? I say i won't need much space because i'm pretty sure i will keep most files on my windows pc. Plus all my games will be on windows for sure so that is another reason my linux drive won't need to be very big. Is SSD worth it? I might not spend much time in linux so i fear i would regret buying an ssd. Also i have another question. Is there a way i could put all my music/movies or anything else into a partition or drive that both windows 7 and linux would have access to? that way i wouldn't have to copy over 100 GB of music and movies. I could have everything on one drive or partition that both OS's could access. Damn now that i think about it i should just buy a bigger HDD and make a partition for linux, and a partition for music and movies.

Thanks for all advice and explanations!

To sum up that unorganized thought process, i need advice on what to buy, and how to set up the partition or hdd that can be accessed by both linux and windows 7.