No, you should be able to choose a file from your own pictures file.
I'm afraid I don't understand that; when you click on New Topic you should get the box to put your text in and underneath that there should be a 'Browse' button. When you click on that it will open the last set of files you last used, maybe Pictures or maybe not, but you should be able to choose 'Pictures' from the list of options on the left.
If you're not being offered a 'Browse' button I don't know what the answer is.
If you want you can start a new post but just put your Heading and your Text in the box then if you mail me the picture you want to post (
norman@snape.karoo.co.uk) I'll put it in for you?
When you first questioned this you said you were offered an 'Attach' button. Directly beneath that and before you do anything it should say 'Browse' then when you click that it should say 'Choose File'; does it offer you your pictures file? It may be offering you other files, say your Documents file, so you first have to click on 'Pictures'. Then you either double-click on the picture you want or you click on it then click 'Open'. What happens then? It should fill in the name of the picture you've chosen then when you click on Post the picture should be there with your text.