One of the good things about the DSLR systems Rosie is that most of the bits are interchangable within the same brand. So if you go for a D50 and then start to build up a collection of lenses (a life's task) then decide to upgrade the camera the existing lenses just attach to the new body. Flash systems and other goodies are mostly the same. It lets you spend the money where it's most important (the lens) and only have to worry about upgrading the camera when you start pushing it beyond its limits.

There are some places that will rent you a lens if you have a specialised need. You might ask when you'd ever need to do this, but suppose you were going on a safari one year. You might prefer to rent that 400mm f/2.8 with a TC20 rather than shell out £7,500 for a lens you're only likely to use for two or three weeks.