How did you "download photos to iCloud"?
If the photos captured by your iPhone 4 are in your iCloud photo stream, it shouldn't matter if you don't have iCloud enabled on your Mac or don't have Photo Stream enabled with iPhoto on your Mac. Turning Photo Stream on with your iCloud settings on your iPhone 4S should make your Photo Stream available on your iPhone 4S, and the same with turning on iCloud on your Mac or by turning Photo Stream on with iPhoto on your Mac.
Not sure why iPhoto doesn't recognize your iPhone 4 if there are photos/videos available in the Camera Roll.
I downloaded the photos to iCloud from my iPhone4 via wi fi while in the ATT store just prior to getting the iPhone 4s. On my iPhone4, the Christmas party photos are on the camera roll and also on the photo stream. On my iPhone 4s, there are no photos in the photo stream. However, the photos that I took at a concert last night did upload to iCloud and are visible in the photo stream on iPhoto. The Christmas party photos are not on the iPhoto photo stream.
So, where in the iCloud are the Christmas party photos? --- I should've just emailed them to myself the old fashioned way.