(1). Depending upon your specific B&W G3 and which motherboard and its’ processor speed (more info needed) it may or may not use larger capacity drives.
http://lowendmac.com/2010/sata-and-ssd-options-for-g3-and-g4-power-macs/ (So some overall size restrictions may apply.)
(2). You may (most likely) need a suitable CD boot-disk from which you might format and install your chosen OS from… to the DOM for use.
(3). Count the male pins on your current HD connector and make certain that the same number of females are available on your targeted DOM, or you may find that you need an adapter.
Is your current machine capable of multi-drives? Or is there only one HD connector cable present? Once you’ve determined your machine’s processor speed, this will answer such questions.
There have been many examinations here of DOMs vs. other types of SSDs and most recently the cost of the DOMs vs. the performance of other SSDs has noted the DOMs being less than beneficial in cost vs. performance. Thusly, the question is… what exactly are you intending to use your machine (and this possible DOM) specifically for and whether or not another SSD may be more beneficial for your intended end-use?
I might suggest that you submit a post to the thread
http://macos9lives.com/smforum/index.php/topic,1991.525.html and tell us all a bit about yourself, your background and your machine and its’ intended use. Then there are many here that may help you going forward.