In reply to edd78: You can get snow in Scotland (and south of the Border for that matter) at any time of year.
I've been on Ben Nevis in May when there was quite a lot of snow about, and even seen small patches in August (although they wouldn't cause you any problems).
Best to look at good weather forecasts which give plenty of detail (try mwis.org.uk) and go prepared. If you find that conditions are more difficult than you expected (and this need not just mean snow) then be prepared to alter your plans. There's no reason why you shouldn't manage a good day out even if you are unable to summit.