Not sure that I follow completely. Do you have a background, that you filmed against, and want to replace that with white?
If so, you might be able to pull a Key on that background, but not being a green, or blue screen, it'll be tough and a lot of hand work. Not sure that the Keying in CS4 will be the best tool. Do you have AfterEffects?
Another process would be Rotoscoping, and AfterEffects CS5 has a new tool, the Roto-brush.
Let us know exactly what the situation and desire is, please,
[Edit] This TUTORIAL might be helpful.
Thanks Bill... Yes, I have a background, that i filmed against, and want to replace that with white.....surprising that there is no easier solution in cs4....perhaps in after effects or premiere...if you shed a light on the details as how to do this would be great
Well, PrPro does offer some Keying tools. Ultra (in CS3 and now back in CS5) gets high marks around here, as does the Keying in AE.
The challenge is that these are designed to work with a well-lit, single "odd" color background, like a blue, or green screen. The Green has become popular, because it is not a color found in skin tones, or most clothing, so it's easier to separate it out. The blue does appear, especially in clothings (think of the TV weatherman where the map shows through his jacket, or shirt).
With a "real world" background, things get a lot more tricky, and the work can be intense, all the way to frame-by-frame masking. For a still, creating a Mask is not that tough in Photoshop, but we're talking about a lot of Frames here, and with subject motion, a new Mask must be done for each Frame. To get an idea of the process, I'd see Rotoscoping. This is a process, that has been around for a very long time. Today, software helps, but there is still often a lot of work involved. Photoshop-Extended offers a bit of help, as it handles motion footage to a degree. AfterEffects offers even better tools, especially with that Roto-brush Tool, that I linked to. Even without it, earlier versions of AE had some pretty good tools.
Though not quite as good, there is Keying in your version (CS4, IIRC?) of PrPro, going from the Garbage Matte and up to it's Keying Effect, though many feel that it pales to the Ultra, or those tools in AE. Here is another Rotoscoping TUTORIAL for AE.
Your problem will be pulling the Key from real-world background, as you cannot Select on a color specifically. It might get down to Exporting as a Filmstrip, and then Importing those Frames into PS, and doing a Mask (lot of Masking Tools there) for each Frame, where there is a change. Again, this is a lot of work, and must be repeated over and over.