Lol i havent a clue what im looking for so ill take it somewere and find out :p

They currently have a width of 205 and a aspect ratio of 50,
rim size of 6.5j
rim diameter of 15 inch.

This is a good tool to use to work out what tyres you need: http://www.miata.net/garage/tirecalc.html

For example, my original 16" FR wheels fitted with 205/45/16 rubber and your new wheels fitted with 205/50/15 rubber = speedo will be 0.8% too fast (nothing really!)

If the tyres are OK then they are the right size!
 
So ill have to wait and see what size my current tyres are on them then???

Can't really tell from your sig pic but if they are 16" they will be fitted with 205/45/16 tyres. If they are 17" then they will be fitted with 205/40/17 tyres probably!

You can reduce the tyre width slightly (less than standard = more stretch)