Is there any tutorial on how to make really good-looking jerseys out there?

try this URL for a great guide...
www.fifacentrespot.de/guide.htm
all you need to know about editing FIFA 99 jerseys!

thanks!
...even if the URL wasn't quite correct...
it's www.fifacentrespot/fifa99/guide.htm
so I went to the main page and looked up this page

sorry, I forgot the extra folder information in the URL!
WHOOPS!
Glad that this helped you...