No, you can't do that in 2003. SW 2005 has a stretch/twist command, but this is not how you would use it
This "can" be done, in assembly mode, by putting the target part in "edit part" mode, and creating a "cavity" feature using the other part as a cutting tool. This isn't the most desirable way to do this though. This method is most often used to design molds. If you want to use booleans, do it using multi body parts.
Vanilla ACAD or MDT ?? If MDT then there will be "some" methods and basic concepts that seem familiar.
If plain ACAD then, trying to apply these methods is like trying to burn diesel fuel in a gasoline engine, it just don't work. There is a section in the help that gives some anologies for commands and such, but many of them do comletely different things.
SW has three very distinct, seperate, (but interconnected) environments, part, assembly, and drawing. In ACAD an assembly is just a collection of objects in the same room. In SW it's a seperate room with a seperate set of rules.
If you plan on "really" learning SW, spend fifty bucks and buy this book.