It's a little confusing the first time through because no product says 'Symantec Installation Manager (SIM),' but that's what it gives you.
To download Altiris 7 tools using Symantec Installation Manager:
Go to symantec.com/downloads
Click Trialware, then choose a program. I chose Client Management Suite under Infrastructure Options
Click the Trialware button
Log in with your account, or create one if you don't have one yet
After logging in, click I Agree
Click No, No Plans, Not Involved to all questions, click Continue
Click Download Now next to a product; I chose Client Management Suite 7.0 SP2 when I needed SIM
A new window opens; click Download Now again
A download window for symantec_sim.exe appears
Click Save and browse to a location to save the file
Click Save
Now run the symantec_sim.exe on the server you're planning to make your SMP. It's from here that you'll download all solutions in the Altiris 7 family.
Hope this helps.