Version 2 and 4 can coexist on the same machine without any issues.
While it is currently possible to migrate footprints from PCB123 v2 to PCB123 v4, no schematic symbols can be migrated.
To add the v2 footprint libraries to your v4 installation:
1. Close all PCB123 programs.
2. Locate your v2 Lib folder, which defaults to C:\Program Files\PCB123 V2\Lib.
3. Copy the contents that you wish to add, or copy all contents. If you have created any parts, you may have saved them to the Custom folder.
4. Locate your v4 Lib folder, which defaults to C:\Documents and Settings\All Users\Application Data\PCB123\Lib\Custom in XP or C:\ProgramData\PCB123\Lib\Custom in Vista.
5. Paste the items that you copied from v2 into the corresponding location in the v4 library.
This will allow you to use the footprints from v2 that you are familiar with.
You can create symbols by clicking on the Main Schematic tab at the bottom of the page, then selecting DesignSymbol Editor. Once you have created your symbol it should be attached to a footprint to form a complete part. This will allow you to find the part in the taxonomy and then place it on your schematic.
1. Click on the Add Part button
2. Click Manage Parts.
3. Click Select Symbol
4. Type the name of the symbol you created then click GO.
5. Click on the symbol name in the Static field.
6. Click Assign Symbol.
7. Click Select Footprint
8. Find the footprint you wish to use using the search parameters. (Alternately, you could first create a custom footprint from the Layout.)
9. Click Select to set the footprint.
10. Add a Manufacturers Name, Manufacturers Part Number and Digi-Key Part number(optional)
11. Click Create New Part and indicate the folder in the Taxonomy you want to store it in.