D.C.
Hi C.,
No, you don't have to wean before trying for #2. There are lots of mothers who continue to nurse while pregnant, although for some, their nipples are really sensitive while they are pregnant and they wean because it hurts to nurse. I can't provide you with any experience because I only have one child and I haven't been pregnant while nursing.
The www.kellymom.com site has a lot of useful breastfeeding information. Here's a link to the site on tandem nursing
http://www.kellymom.com/bf/tandem/index.html
If you decide to wean, here is the site on weaning.
http://www.kellymom.com/bf/weaning/index.html
Generally, it's best to cut out one of the remaining feedings every few days. If you're going to wean, you might start out by limiting nursing to only after waking up and just before going to bed, then only one of those two feedings, and finally, eliminate the last feeding.
I understand how you feel. My daughter is 18 months old, and I'm getting pressured by my husband, mother, and mother-in-law to stop nursing. Neither my daughter nor I are ready to stop.