900MB of memory sounds about right, so nothing out of the ordinary there.
Is the CPU usage just while the process is starting (which is expected) or is it like that even JBoss has started and is idling.
It can take 2-6 minutes for JBoss to start completely, it needs to unpack and load a very large number of compressed war and ear files, plus various other tasks.
To see if JBoss has finished starting, open the C:\Adobe\Livecycle8\jboss\server\all\log\server.log and look for a line like:
2007-11-27 10:53:41,535 INFO [org.jboss.system.server.Server] JBoss (MX MicroKernel) [4.0.3SP1 (build: CVSTag=JBoss_4_0_3_SP1 date=200510231054)] Started in 3m
Once you see the "Started in xyz" part, the CPU should drop down to 0-5%.
I like to put a batch file in my start up folder, so that as soon as I log into the server, the tail -f of the log pops up. You can get the tail command from the Windows Server 2003 Resource Kit (which you can install on XP). This saves you having to keep reopening the log file to check if the server has started.
By the way, that start up time I posted of 3m:50s was on a fairly new Xeon processor with 2GB of RAM and a fast RAID array, so on your laptop I would expect a start up of 5-6 minutes or more.