Not sure about Bondi but you can windsurf from most of Sydneys beaches. Its just that some of them are pretty tricky to launch from in certain conditions.
Wanda is good for summer sea breezes and southerly fronts, the local guys will be able to help more.
On the northside Palm Beach works in most winds on both the surf side and flat Pittwater side.
Newport is sailable but you need local knowledge as it can be tricky.
Collaroy works well in a SSE wind and has the option of sailing out to the breaks off Long Reef headland, again local knowledge will help.
I know guys who sail Manly but being so crowded it might not be fun.
They also have a great surf school.
You can hire gear from Wind surf n snow at Collaroy, call on 9971 0999.
Hope this helps.

forget Bondi and the other city beaches (leave it to d%$less kiters) - even the southern corner at Bondi is protected from the NE - for an intermediate stick to the harbour - Rose Bay in front of the sailing club - but as KA 43 said hire gear is only from WSS so your on the North side already

Why would you want to sail from a crowded beach anyway?