From the introduction:
Shadowrun, Fourth Edition (SR4), presents a completely new rules set from the previous Shadowrun, Third Edition (SR3). For this reason, we strongly suggest that if you wish to convert your player character that you simply re-build the character using the SR4 character creation rules with an adjusted amount of Build Points.
For a quicker conversion, without re-creating the character, follow the guidelines below. This will result in approximate conversions rather than exact duplicates, but this process is easier and accurate enough to satisfy the needs of the game.
If you simply need to convert NPC stats, we suggest using the quick conversion rules.