You are very lucky, it seems that you can pick the one you like.
In order to help you with this task here are some links, that should
help you to make an informed decision.
The SuSe Linux 7.0 distribution is quite complete, you have 4 ISOs to
download. You can grab it at
the following URL:
ftp://ftp.suse.com/pub/suse/sparc
TurboLinux
Workstation 6.1 for intel ships with a
SPARC developper release CD.
To install Linux on a SPARC based computer, should be strightforward
if you follow the informations provided by your distribution.
To boot from a floppy drive you have to have an install image on a
floppy disk and to issue the boot floppy from the OpenBoot.
If your workstation does not have a CDROM or a floppy drive, you can always try
to perform a network installation using NFS as explained by
this French document:
http://www.linux-france.org/article/materiel/sparc-install/Sparc-netinstall.html
. Basicaly, you have to set up an NFS server and to boot your
workstation using the
boot net vmlinux nfsroot=192.168.52.12:/tmp
in order to access the image that is exported by the
192.168.52.12 workstation on the /tmp directory.