Most basic 2-stroke engines will run okay on a ratio of about 30:1 two-stroke oil to petrol. If no better answers come along, try that. If you err on the side of caution you won't go far wrong. Too much oil, and it'll just smoke a bit. Too little oil and it'll seize.
My boat engine runs on about 40:1, but that's expensive synthetic oil on a Mercury 200 V6. Doesn't really matter what type of 2 stroke oil you use on your engine as it's pretty lightly stressed and low tuned. Just 2-stroke that you buy in Halfords will be fine. 30:1 would be a good guess I'd say.
Hope this helps.
Graham., May 2007