If I got a SSD, then would I need another drive also in the MB, and I take it that I would have to re install windows or could I just clone?
You can clone, however you might run into trouble since your current windows partitions are probably going to be larger than your new SSD. Honestly, when moving to an SSD, I suggest a format and reinstall. This way you can be a bit more critical of what you actually install onto your rig and you can ensure the best performance by not installing a bunch of stuff you don't use.
At the moment I have 286GB used on my hard drive, and it needs space to work, does a SSD need space to work?
Of the 286GB on your hard drive, how much can be attributed to things like music, internet downloads, videos, isos, games, etc. It's surprising when you look at Windows and the majority of apps that you install and use...aside from games...they usually aren't huge. Even with a game or 2, my SSD usually has about 40GB installed at any point in time.
How big does it need to be to just install windows?
20GB of so for the install, and plan space for updates and such. Honestly, I would earmark no less than 40GB.
Would I put all the other programs on a second drive that I connect to the MB?
You could, but for best performance, you want to install the applications themselves directly on the SSD. This way you benefit from the speed increase. Unless you buy and run a ton of commercial software and games, the amount of space used by programs probably isn't that huge.
As I recall Windows takes up 16-17GB. You should install the OS and programs on the SSD and move all user files to a mechanical hard drive.
I'm unsure why everybody suggests moving their user files to the mechanical hard drive. In most cases, I would think things like word doc, excel spreadsheets, text files and the like are all going to be pretty small and not amount to a lot of used space. The things which take up the most space are music files, picture files, videos and downloads. You can easily just save these to your mechanical drive and set your browser default download location to your mechanical drive.
Most programs need to be installed on the SSD as they write entries into the registry.
Actually you can install these programs usually on any drive you like. Writing files into the registry has no bearing on what drives you can install software to. If you install a piece of software onto your mechanical drive, the registry keys for that software will simply point to the drive letter of the mechanical drive.