I need something small maybe 49 keys at the most. Preferably with some decent sounds built in such as piano, elec piano, strings. If I can play rythms like an arranger that would be a great plus.

I saw several midi controllers such as CME U Key, E-Mu, etc.

It will be great if it be connected to a standard XP laptop. But I do not want to buy soundcards or MIDI. Can the laptop be used as sound source and rythms ? Use the buttons on the keyboard to control the variations and selecting sounds ?