DV Info Net - Will Older Plug-ins work with CS4?

As one who is contemplating moving from Liquid 7.2 to the Adobe CS4 Suite I have a question about older plug-ins.

I went over to the Boris site and got a severe case of sticker shock. With Liquid I had all the effects it came with plus the Hollywood FX package thrown in as well. The cost of additional Plug-ins was something I never had to deal with.

If any of you are buying these packages for a personal hobby as opposed to using them to make a living your stomach is far stronger than mine. Boris Continuum Complete is $1000.00. As someone who does this as a hobby that price tag is a little higher than I would prefer, especially since I don’t have to have the latest and greatest to make me happy.

My question is will the plug-ins made for the Adobe CS2, CS3, or CS products work in CS4 assuming you are buying a legitimate copy with original discs and packaging?
I am guessing these products have to be activated like everything else so you had better have all the original materials.

I assume you can buy older used copies like those mentioned above for a fraction of the cost of the new ones on sites like Ebay and other used software retailers. But it will do me no good if I buy them and discover they won’t work. If this is a stupid question please forgive my ignorance.

My only experience has been with Liquid and the same Hollywood FX package stayed compatible with ongoing updates without any problems. But knowing that does not tell me if the same applies for other NLE products. I searched the forums as I thought this might have been a question some had asked before but I found nothing about it anywhere.

If you have to buy CS4 plug-ins for the CS4 Suite then I will get them. But instead of buying everything at once as I had planned I will probably spread the cost of my migration over six months rather than blast my credit card to the moon all in one hit.

Thanks.