As iTunes is constantly being updated the steps below may not be current so please proceed with caution.
- Open iTunes on your current PC
- Click on Advanced and then 'Consolidate Library'
- Close iTunes
- Copy the iTunes folder to a Server or USB drive
- Go to the new PC
- Install iTunes
- Remove the iTunes folder
- Copy the iTunes folder from step 4
- Open iTunes
The following CNET video is very useful.