Link to popup with defined size

Hello everybody!
Can someone please help me with this one.
I want a link to open in a popup with a fixed size. I just cant get it to work.

'<div class="mPrice"><a href="'.zen_href_link(FILENAME_CREATE_ACCOUNT, 'level=VIP').'">'.sprintf(TEXT_MEMBER_PRICE_LINKED, $currencies->display_price($whole_prices[2], zen_get_tax_rate($product_check->fields['products_tax_class_id']))).'</a></div>'

The code above gets the memberprice of a specific product and the text is linked to the Create Account page.
I want it linked instead to /shop/myfiles/medlemspris.htm and opened in a window with size 300x300 px.

how shall this be done? All my attempts make the site hang?
Just to give you something to laugh about i show you my attempt. What is wrong with this code?

'<div class="mPrice"><a href="/shop/myfiles/medlemspris.htm" target="_blank" onclick="window.open('medlemspris.htm', '_blank', 'width=600,height=600');return false;">'.sprintf(TEXT_MEMBER_PRICE_LINKED, $currencies->display_price($whole_prices[2], zen_get_tax_rate($product_check->fields['products_tax_class_id']))).'</a></div>'

Please help me!
/Jagge