you need to add this field as look up field on following two views in CRM 4.0
1. Account Lookup View
2. Quick Find Active Accounts
so add this fields see following steps
1. go to customization open account entity
2. open Account Lookup View and click on Add Find columns
3. select your column and click on save and close
4. do same thing for Quick Find Active Accounts view
5. save and publish entity
MayankP
My Blog
Follow Me on Twitter