I have the computer program (NASCAR 2003)
I can beat the crap outta most of the drivers.
Should I be in a real race?

Seriously though. I love SIMS. I have one that I use occasionally and I think it helps alot.
As MIKEL states it's great for twidling sticks etc. It's easy to try new stuff out and find out if your capable of handling it. It's also great fun to push the limits without the worry of crashing and I believe that makes us better pilots. My point here is.
AT LEAST SPEND ONE AFTERNOON WITH A REAL PERSON THAT IS KNOWLEDGABLE IN THE HOBBY!!!!!!!!!
My reasons for this are endless /engine tuning/battery checks/control setups/linkage security/adequate protective foam/wing banding etc etc etc/
If nothing else an experienced helper can educate you on the proper (after crash beverage)

Also if you notice I didn't say "INSTRUCTER" many new guys think an instructer needs to be this AMA certified, NASA trained, FBI cleared, FAA approved, AA convert, that has been drillin holes in the sky since Jesus left his last footprint. NOPE!!!!!
Ask around a little and I'm sure you can find somebody (even if they have only gotten in one season of flyin) that'll give ya a couple hours of their divine intelligence... (It'll help a bunch)
Add that to your SIM time and you'll be flyin!