Your MacBook Pro installer discs can't be used to install 10.5 on your eMac.
Boot Camp won't work on an eMac. Alternatives for Windows exist on my FAQ*:
http://www.macmaps.com/macosxnative.html#WINTEL
Access to booting Mac OS 9 is not limited, but Classic is. You must either put 10.4.11 or earlier on a second partition, or external Firewire hard drive, if you wish to continue using Classic while having 10.5 on your system. The difference between the two is outlined in my FAQ*:
http://www.macmaps.com/macosxnative.html#CLASSIC
To install Mac OS X 10.5 if there isn't a built-in DVD drive, you must either use an equivalent age eMac to install if that equivalent age eMac has a built-in DVD drive, or an external Firewire DVD drive from
http://www.macsales.com/ or
http://www.xlr8yourmac.com/ that is known to be able to install 10.5. See my user tip:
http://discussions.apple.com/thread.jspa?threadID=1418365&tstart=0
- * Links to my pages may give me compensation.