The Motorola SLVR L7 is supported now as an iSync device using either a USB or Bluetooth interface, but only with iSync 2.1.1 and OS X 10.4.4 or later.
The short answer, therefore, is that you will have to upgrade your hardware before you can install the software required to support your mobile handset.
If you are looking for a low-cost upgrade path, Apple periodically offers refurbished machines [with full year warranties and current OS packages] at about a 15% or so discount off of retail prices. Currently, a 1.9 GHz iMac G5 17-inch SuperDrive-equipped model with a 160 gigabyte drive is available for $ 1099.00. This package is iSight equipped, and includes FrontRow.
To find deals like this, go to
http://store.apple.com and look for the red SAVE tag in the right sidebar.