Welcome to SRB2Wii.
1. Download the version of SRB2Wii you want (at the moment I recommend the IOS version since that version works best right now)
2. Extract the BZip2 compressed tarball (using 7-Zip preferably). The resulting folder will contain two folders that need to be on the root of the SD card.
3. Copy your SRB2 data files, which need to be copied to /srb2wii. The SD card should be laid out like this:
(FOR SRB2WII/IOS)
/apps/srb2wii/boot.elf
/apps/srb2wii/icon.png
/apps/srb2wii/meta.xml
/srb2wii/drill.dta
/srb2wii/knux.plr
/srb2wii/music.dta
/srb2wii/rings.wpn
/srb2wii/soar.dta
/srb2wii/sonic.plr
/srb2wii/srb2.srb (or srb2.wad)
/srb2wii/zones.dta
/srb2wii/tails.plr
/srb2wii/filesystem.tar.bz2 (or filesystem.img after a bootup)
/srb2wii/swap (after a bootup, if this isn't there when you haven't run it yet its fine)
/srb2wii/base_config.cfg
/srb2wii/wminput.conf
Once SRB2Wii has started up at least once, the new folders /srb2wii/addons (which houses WADs) and /srb2wii/log (which houses system logs), and the new files /srb2wii/filesystem.img (which houses the main filesystem) and /srb2wii/swap (standard swap space) will be created.
Once SRB2 itself has started at least once, a new folder called /srb2wii/.srb2 will be created, which will have gamedata.dat, srb2log.txt and srb2sav*.ssg (config.cfg gets generated every time SRB2Wii starts up so this is never there, the base config file can be found at /srb2wii/base_config.cfg on your SD card).
Download links:
Binary (IOS version, for the Homebrew Channel):
v2.0.0rc4 (r6115) -
http://repos.srb2.org/srb2wii/srb2wii-ios-2.0.0rc4.tar.bz2 (11.1MB)