I don't advise it with IE since it's not built in... You will need a work around or similar.
With FireFox, you could do by writing a small bat file. Instead of opening the browser, you'd have to run the .bat file which will open FireFox with the chosen tabs
START %BROWSER% -new-tab "google.com"
START %BROWSER% -new-tab "http://superuser.com"
START %BROWSER% -new-tab "stackexchange.com"
Personally, I'd save several different versions (for each of the week). You could even have a script to open the page when you first log on in the morning.
If you must use IE, you'd use a similar concept in that every day, when you first log on, you'll run a script which will update the registry for you. Save the below as a .reg file and run it (remember, take a back up first just in case)
Windows Registry Editor Version 5.00
reg add "HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main" /t REG_MULTI_SZ /v "Secondary Start Pages" /d "http://www.bbc.co.uk\0http://www.superuser.com\0" /f
So, you will have 5 of these files and for the entire day, when you open IE it will have the settings you want.