DHCP lease delegation is done by the server, not by the client. So either your reservation is wrong (typo, or server not restarted to pick up the reservation), or your client isn't using your server.
The only exception to this rule is if the client already has a lease. Sometimes it will ask the server, "can I renew this existing lease?" and the server will say "yes, you can keep using it." Most of the time though the server will say "no", forcing the client to begin the dhcp process from scratch, resulting in the reservation being issued. (Sometimes when the server says "no", the client just hangs on to the lease until it expires before starting the dhcp process over again.)
If you set your dhcp server's syslog to pick up
*.debug, dhcpd will drop all kinds of detail into your messages file and you can see exactly what it thinks is happening.
Google suggests you can release/renew your lease on the Solaris 10 system by doing this:
# ifconfig nge0 dhcp release
# ifconfig nge0 dhcp
nge0 is whatever your ethernet device is.