For those (like me) that got a little confuse; fink can be found in /sw/bin (I know the info is out there - just took me a while to figure it out)
The fink installer tries to set the path to /sw/bin but in my experience it fails at this sometimes. To run either fink or apt-get, it's a good idea to include the /sw/bin/ path to them.
With PowerPC, you probably want to use apt-get so it installs the binary GTK packages. With Intel, you currently have to use fink in order to download and compile the packages' source.
Note that until binary packages are available for Intel, if you want to distribute a GUI app you create with Laz to other Intel Macs, you'll need to have the developer tools installed on those other Macs (in addition to X11) in order for fink to be able to compile the GTK packages! On PowerPC Macs, your users don't have to have the developer tools installed since apt-get will download only the binary packages and no compilation is necessary.
I find the whole fink process extremely confusing and error prone (plus fink and fink commander appear to be buggy). This points up the importance of one day having the native Carbon widgetset both for compiling Lazarus IDE and for compiling our GUI apps in Laz so we can drop this whole X11/fink/GTK requirement for OS X!
If we developers have problems with fink, imagine what kind of problems your users will have if you ask them to install fink and GTK themselves.