Upgrade Vista to 7 New hdd ??

Sorry if this is posted already but I have read for hours and can't find my exact issue.

Bought a new retail HP back in 2008 that had Vista pre-installed. Did NOT come with a windows cd/dvd.

I'm wanting to upgrade to Windows7 which is easy enough, just buy the upgrade dvd and install. I have no issues buying the upgrade.
But what I'm wanting to do is buy a new SSD AND upgrade to Win7. Then wipe the orig. hdd in the machine as a storage drive only.

I also know I can buy the Full Ver of win7, but I don't want to spend an xtra 100$ and don't think I should have to just because I want to upgrade my hdd.

So the question is, is there a workaround to achieve this?
Or must I spend the extra 100$ just to get the full version?

Thanks in advance for any input

ok thank you, i will check that out. but to add...
this will be like a new install since i am replacing the hdd with a ssd. so i'm a tad confused on how the upgrade dvd will know that i have vista already. this is pretty much a new pc build which brings me to another question actually. sorry.
i was watching windows weekly with leo laporte and they were talking about OEM vs Retail. am i understanding correctly that i can order win7 OEM from say tiger direct along with my new ssd and be up and running?
thats really where i am currently... new build, all new everything except hdd which has vista on it, and i want to buy a new ssd and upgrade to win7. so can i just get the 99$ OEM or do i have to buy the 199$ Retail is the main question. Sorry for all the confusion.

New mobo too.
Here is what I have done.
Bought new retail HP desktop back in 2008, it came with vista. I activated as required. Been using ever since.
Now: Built new pc- case, mobo, cpu, ram, gpu, psu.
Took HDD from my HP vista machine and put in new case to use temp. Working fine BTW, so I don't understand the mobo thing. It did seem to "think" for a little while when I made the switch and did install some new drivers, but never ask for a windows cd or anything.
So now I am ready to order a new SSD and Windows 7 this week.
I still plan to use the HP's HDD in new machine, but I want to have the new SSD with win7 as the primary, and wipe the HDD that was in the HP and use it as 2nd, or slave just for storage.
Just trying to make sure I order the correct DVD of Win7.
I don't wanna spend 99$ for the OEM only to find out I should have bought the 199$ retail. You see?
But I don't wanna spend 199$ for an OS either.

phantomrider said:

so i'm a tad confused on how the upgrade dvd will know that i have vista already.

It won't.

It's accepted on faith.

Vista doesn't have to be installed.

You certainly don't need a "full" copy of Windows. "Upgrade" is fine.

A new OEM license will work fine and is cheaper, but most would tell you to buy non-OEM if you think that you might change motherboards at some time in the future. At times, you can get away with an OEM license after a motherboard change, but I wouldn't count on it.

I guess to avoid confusion I should have just said building new pc and want to install Windows 7, then ask which to buy, retail or OEM. But I get the gist. And thanks for all how provided input.
I went ahead and ordered the OEM DVD and will see how it goes.
Thanks again.