i still got mr spiv's original multifirmware, and i like it, but i hear great things about aqua's firmware, mr spiv's however is the easiest to flash with i think (based on what i hear from others)
Xvid encoding for gpcinema: http://www.btinternet.com/%7Ewaystation/gpcin.html
Divx encoding for gpcinema: can't find the site, search a bit on google, there's a good divx tutorial somewhere out there