No, not cars.
Boosting is a form of multi-boxing. Sorta. It probably can not be considered true multi-boxing, but many multi-boxers use it to get their teams leveled quickly if their aim is to work on heroic/raid multi-boxing. Boosting is also a great way to level an army of alts. Or maybe it's more like a small contingent of alts.
I'm currently working with three accounts and am writing this from that perspective. However, this can be easily tweaked for two, four, or five accounts with probably no real changes aside from how you set up Recruit-A-Friend and whether or not to use Jamba if you're only dual-boxing.
What You Will Need
Look through your myriad of 80s and decide which toon will be the one to do the boosting. The best options for this are tanking classes however anything could potentially work, just not necessarily as quickly. I respecced Laurewen from Balance to Feral and threw her into her tanking gear (a mixture of heroic and emblem gear with some TOC and ICC cast-offs). I've heard that Protection Paladins and Blood Death Knights are really good, however Warriors have more trouble due to having significantly less self-healing. Be prepared for downtime.
Another possibility is a warlock; simply throw one or two DoTs on each mob, tabbing as you run. This will require a different strategy for pulling than a tank would utilize.
A freshly-pardoned Death Knight (~58) is a great booster for the 10-25 stuff, possibly even SM level. The more narrow level range will provide your boostees with more XP.
You're going to need an account for each toon you want to boost at a time. If you're boosting a pair, like I am, you'll need two more accounts. These accounts *must* be yours; don't borrow your friends' or significant other's as that constitutes account sharing and is against the Terms of Service. All accounts that you're multi-boxing with must be in your name. I haven't been reported for multi-boxing, but I know many who are and while multi-boxing your own accounts is fine, if they catch you sharing accounts you're in big trouble.
I'm assuming these accounts are going to be brand-new, which means you need...
I purchased two Battle Chests from a local GameStop who happened to be selling them for $20 each. This gave me access to space-cows and shamans. If you want to go on and get WotLK for each account as well, go for it, but it isn't necessary.
Keep your accounts secure! If you aren't already using one, now's as good a time to get one as any.
This is what allows multi-boxers to, well, multi-box. The multiplexor allows a key press to be passed to multiple windows, so pressing 1 in you first WoW instance will send 1 to all of your WoW instances. For boosting, you don't need anything quite as sophisticated as a true multi-boxer does. I'm using Octopus which is a bit old but does the job.
Jamba is a WoW add-on that allows organization of your teams. With all of its sub-add-ons, it handles quests among your team members as well as allowing you to keep an eye on their XP/Rep/Health or whatever it is you want to watch. It can also pass whispers from your 'slaves' or boostees to your 'master' or booster so you know when someone has whispered one of your alts.
Setting it All Up
Same Battle.net or different Battle.net accounts?
This is really a pick-your-poison sort of situation. By leaving all of your accounts in one Battle.net account, you can share any account-bound perks, such as that new WoW pet they've announced for purchasing the Starcraft 2 Collector's Edition. However, by leaving them on three accounts, if one is compromised the other two are likely not to be (assuming different passwords, of course). Also, if you use them all on the same Battle.net account, you'll have to wait one minute between logging in each of them due to the Authenticator's wait time. If you use the same Authenticator on three different Battle.net accounts, you can simply copy and paste the Authentication Code into each window. I chose to go with the latter option, but ymmv.
You *really* want to do this. Triple XP and a once-an-hour summons makes boosting a breeze. Add in level-granting and it cuts the time you'll be boosting significantly. Making sure you have it set up properly is crucial or your alts can miss out on their bonuses.
The plan here is to maximize the benefits that you'll be able to gain through RaF by chain-linking your accounts. First, start with your current WoW account, the one with your 80 that will be doing the boosting. Then send yourself a RaF Trial invite! If you're going to use separate Battle.net accounts for each account, be sure to log out of Battle.net before clicking on the link in your e-mail. Once you've got that set up, verify that the RaF link is active and upgrade the trial account to a standard account with the WoW code that you purchased. Now that the second account is active, do the same thing as the first, sending yourself a RaF Trial invite. However be absolutely positive that you're doing this with your second account or the triple XP while boosting will not work!
To sum it up in short,
A recruits B who recruits C.
Next time: Setting up Jamaba, Octopus, and the Boosting method