There are a number of Linix "Live CD" distributions out there. These allow you to boot Linux from a CD and run it (somewhat slowly) without ever touching the hard disk in the machine. (They can access the disk however, which makes them good for system repair, both for Linux and Windows.) One popular one is Knoppix, and Mandrake makes one called MandrakeMove, which takes the important next step of letting you store your personal config choices on a USB thumbdrive or floppy. There are distributions that can fit on a thumbrive (after all, those drives are getting quite large for little money, but this is recent enough there hasn't been as much focus on this.)
Let me suggest where I would like this trend to continue. It's great to be able to take any machine and quickly convert it to your style and environment with a CD, or even better a business-card CD or thumbdrive. (Most systems can boot from a CD, fewer from a thumb-drive, most from a floppy leading to another device.) Storing some state on a floppy, thumbdrive, CD-R session -- preferences, home directory files and scripts, browswer config and bookmarks -- is a must. Indeed, if the tools let you build a custom CD just for you with your choice of packages you can bring in much of your whole working environment.
I haven't seen anybody provide automatic storage on the net, based on the assumption the machine you take over probably has an ethernet card. If it does, it would be great to go out and suck down your latest personal changes and files, starting with the most important to get you going, and bringing the rest in the background. This doesn't need a special server, though the group making this distribution might well offer to do so. You could keep and update much of this data in a special mailbox message or mailbox folder, especially with IMAP. Anybody can get access to that. (Or a web mail tool like GMAIL.) Of course if you have actual hosting this can also be used. The data would be encrypted, you would need a password -- not just your mail password -- to use it.
As you changed the data it would be updated to the net storage. Now you could go to any machine with a non-customized CD. Indeed, you could even, on a common fast machine, download a minimal environment (perhaps 60 megabytes which is just a few minutes on a fast broadband link) and after it boots, get the custom information including which other packages are important.
The key is to do things in the Windows filesystem, most likely to be what you find on the machine where you are the guest.The distribution should look at the local disk, and feel free to grab some spare space if not told otherwise. It can release this space at the end if need be, or keep some or all of it. Most modern machines have gigabytes free for temporary use. In that space create linux filesystems, and copy into them the portions of the filesystem that must be read/write, as well as personal files and updates sucked from the net. Perhaps have two filesystems, one of which is "keepers" that would live on the machine if you planned to use it again and had permission to take the space, and the other more temporary space.
Right away you would move to cache any programs read in from the CD-ROM, just for speed. This might be disposed of or kept. If you don't have a CD-ROM, you would download a kernel and a root filesystem onto the windows machine, and get a bootloader on floppy (or other medium) which is able to load that kernel, decompress that root and get it going. If you had a CD, you would boot from
the CD and start running applications from the CD but cache them to the hard
disk. If the hard disk had many free gigabytes, a background process might unpack all the files on the CD. If your CD is custom, to your own tastes, it could follow other routes.
Given a machine with a fast net connection and spare disk space, you could in a few minutes be booting up something hard to tell from your home environment, and in which changes would be synced back to your home environment. Your browser would act just the way you like it, as would your tools. You probably can't port all your files into the system, though one could build a system which gets them on demand if your system remains up and accessible in this fashion, but in that case you may find it simpler to log onto your remote system.
Finally, the whole thing could also be packaged up for easy deployment as a network bootable distribution, so if there is one computer hosting the distribution, any computer can quickly be network booted to act just like your home machine.