Go to CS6 or LR4 Thoughts
Lightroom 4 will certainly work with Photoshop CS5. When you first start using it, Lightroom will warn you that it requires ACR 7 in order to ensure that all adjustments will transfer to Photoshop. Then it will give you the option to render a copy that includes the Lightroom adjustments. That is the option that you will want to use.
Lightroom does not resize your images. However, there is an export option that will enable you to export copies in different file formats, levels of quality, and sizes. Your original images are your "master" files, and they are never modified. The changes are stored in the Lightroom catalog.
You indicate that you have upgraded Photoshop several times which could imply that you are using an older operating system. You need to be aware that Lightroom requires at least Windows Vista. Lightroom 4 will NOT run on Windows XP. That may not be an issue, but I mention it just in case.
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