Yeh it can be very tight to remove, if its loose then the chances are the inputshaft/gear splines are worn and will require replacing. Once you have 5th gear off then its quite straight forward to strip. Just keep everything in order for when you come to rebiuild

If its tight you should be able to remove it with a decent 2 or 3 leg puller. There is also a proper tool available for removing the gear however i cant find any links to it on the net.

Some more useful links...

http://www.quantums.info/gearbox.htm

http://www.turbosport.co.uk/showthread.php?t=135731