Registry only if you need to register file extensions. (I suggest using the installer for that)
If you install, first, then you can update the new installation.
( If you decide not to use the installer: Search for a file "fpc.cfg" (same folder as fpc.exe, see options dialog). Any path changes must then be adapted in thi file to. Better use the installer)
All your settings (vista): C:\Users\USERNAME\AppData\Local\lazarus\
Any 3rd party package, you installed yourself. (You must know, where you did put them))
All your own project sources.
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The lazarus.exe. The new installed one, does not have your added packages. But you can solve by recompile the new IDE.
If any package is not found (due to path changes), just open the package once by hand. Lazarus should remember the new path