Converting Delphi project is a complex task, it may directly work, or it may not, depending what the project uses. You should learn (Object) Pascal first, both the language and implementation (Free Pascal or Delphi compiler).
Regarding XPMan, you can simply comment out or delete, Lazarus doesn't need that just to provide XP manifest. Simply check Project Options->use manifest file to enable themes (Windows only).
For Tnt components/units, you have to check their structure. Using a component / unit means that you need that component / unit + its dependencies and subdependencies. I never use Tnt, but normally components are distributed in a package (.dpk), which you'll need to convert as well (to .lpk).