If you would just like to hide the CMD window, you only need to start Syncthing with -no-console, e.g. syncthing.exe -no-console. Also, you may want to check Starting Syncthing Automatically — Syncthing documentation.
I have a feeling that SyncTrayzor, and especially its built-in browser, will not work in Windows XP anymore. The hardware sounds too old for any newer, supported version of Windows, so I personally would try to run some kind of a lightweight Linux distribution on it.