Uh-oh - he's off with the fairies already...
I'd suggest you keep at the 50mm end rather than the 18. You'll get more control that way. It's pretty common for guys to use an adapter or even tape a 50mm prime lens reversed to the end of a longer lens. Maybe I shouldn't be showing you these, but...
http://photography-on-the.net/forum/...9&postcount=30
http://photography-on-the.net/forum/...6&postcount=39
http://photography-on-the.net/forum/...3&postcount=41
http://photography-on-the.net/forum/...7&postcount=43
You get the idea. Personally, just get yourself a true macro lens and be done with it
I know you're having fun.
These are the sort of reversing ring you need I think. Just need to make sure the thread matches the lenses you want to connect:
http://shop.ebay.com.au/i.html?_nkw=...1&_from=&_ipg=