You may wire an outlet to a lighting circuit. It would be wisest to make both the permanently hot and the switched half on the same circuit, however - to put two different circuits in an outlet box can be quite confusing to someone down the road and can supply 240 volts to the box (US - other countries could be considerably higher).
To make the outlet half hot, however, you will need BOTH a permanent hot wire AND a switched wire, plus of course a neutral. Some switches have the neutral in the box, some do not. Some light fixtures have a permanent hot in the box, some do not. If you are remodeling it can be complicated to get all the wires you will need.
If this doesn't answer you, email me, or wait a few days - there will soon be a new hub on the subject.