Volvo Repair: Dimming of Dash Lights and Head Lights, power steering pump, mechanical ability

Question
I have a '98 S70 (70,000 miles) and during the winter when it is really cold my interior lights and headlights have a tendency to dim and then come back to full strength.  This cycle will continue for a little while until the car warms up and then it will only do it when I come to a stop at a light.  I recently replaced the battery and it has made it better (happens less) but it still does it.  Do I need to replace the alternator?  Is this something I can do my self?  If so are there any instructions out there?  Thanks for your help.

Answer
sounds like possibly a bad alternator,but should be checked to see how many amps it charges.there is a special tool to remove the drive belt but it can be removed without the special tool but it is just a little harder.the alternator is below the power steering pump which will need to be removed.it is not too difficult say maybe a 4-5 on a scale to 10 so if you have fair mechanical ability you could do it.