Is there a way to install all versions of all browsers on one machine?
Yes. I have IE8 Beta2, FF3, Chrome Beta, and Safari 3.1.2 with the applicable developer plugins.
Sure, and the best way to do this is to use virtualisation technology such as VirtualBox.
Why would you want to do that?
Typically, a product wont allow parallel installs (multiple versions of same product, though certainly you can have multiple versions of different products).
If you want to do some analysis or testing , doing that in separate Virtual Machines (check out VMWare) may be an option.
I use virtual machines to do different browser version configurations. I'm assuming you want to test different version of IE, Firefox etc.
If you automate your testing at any point the virtual machines are also handy for having a way to store many different configurations for testing on one machine.
we have used this to install mutiple versions of IE for testing it goes as far back as 3.0
For several browsers, like Firefox or Opera, it is just a matter of copying the original program directory elsewhere and upgrading. Most of the time, the old version should still work.
For IE, there are several distributions, IETester seems to be a complete, easy solution.
I am not sure why you really want this but if you want to install different versions of IE use the following tool: