I have an Automator workflow that does something similar. Each time I run the workflow several web pages, including this forum's new posts page, are opened in a series of tabs. My solution is part of a larger workflow that also launches Mail, iChat and Skype.
If you would like to try it here's the part needed to open web pages.
1. Launch Safari and make sure that it is set yo open new pages in tabs. Sounds like you already have this in place.
2. Download and install this Automator action.
3. Launch Automator. Under Snow Leopard you will be asked what you want to build. Mine is an application but I think it would also work as a Service.
4. Find the following actions and drop them into the right side of Automator's Window
a. Get Specified URLs - Enter the names and URLs for the sites you want to open.
b. Find the "Display Webpages" action. Look carefully at the description in the lower portion of the window. If it says it open the pages in tabs use this action. If it does not say this use the "Display Webpages in Tabs" action that you installed.
Make sure Safari is closed then click Automator's Play button to test the workflow. Ignore the warning message. If the workflow functions as expected save the workflow in a convenient place.
I run the workflow from an alias. I also keep a version of this thing saved as a workflow. That way if I need to add/change urls I load the workflow version, change the urls and save with the same name as the existing application.