It is most likely NOT a monitor profile problem since any monitor profile should be in effect for CS3, CS4, and ACR.
What IS likely the problem is a mis-match in working color space. You probably have a different working colorspace set in CS4 as compared to CS3 or you have the other color settings set in such as way so that CS3 automatically adapts and CS4 doesn't.
Here is what you need to check:
You need to check Edit>Color Settings... in both CS3 and CS4. If you want them to behave the same, they should be set the same. Your working colorspace is a matter of preference. The most common are sRGB, AdobeRGB, and ProPhoto. If you have no idea what I am talking about and most of your images are either displayed online, sent via email to friends and family, or printed at the local drugstore then sRGB is probably a good choice. As you have time to learn about colorspace, you can try others.
I usually use "Preserve Embedded Profiles" for the Profiles section of the color settings and I put the checkmarks in all the "Ask When" options of the Color Settings. That way, PS always reminds me if there is a mis-match coming into PS.
Now you need to check which colorspace ACR is using when it does its raw development. If you look under the image in the ACR editing window, you will see a line of blue, underlined text. Click on that and you can set what colorspace will be used by ACR to develop images. Normally, you will want to make this colorspace match your working colorspace in PS but if you set up the color settings in PS as I mentioned above, you don't have to necessarily. Using the settings above, if you happen to generate an image from ACR in the ProPhoto colorspace and your PS working space is set to sRGB, PS will prompt you to make a decision. You can then decide if you want to use the colorspace embedded in the incoming image (ProPhoto)or the default working space you had previously chosen for PS (sRGB).
If colorspace issues are new to you, they can be kind of confusing at first. You may just want to set both PS and ACR to sRGB and use that for now.