I've downloaded a 10 startup screens package and all of Dragon's Jerseys packs and extracted those to the sgsm folder, but it seems they're not in effect. how should i "install" those?
Make sure they haven't been placed into a subfolder within the sgsm folder. ZIP and RAR files may be compiled saving their original folder paths which are then used when you extract the files.
If they are additional jerseys that don't appear in the original database, some further work is required. If the patch comes with a teamgear.dbf file or a batch file that will add the data automatically, you'll need to carry out that step before the new jerseys will be accessed by the game.