The deal with extended characters on a desktop is that you hold down Alt and key in the the code with the numeric keypad, right? So the the deal is, you need a numeric keypad on the laptop but there ain't one. Look close at the keys. Usually, somewhere in the 'J-K-L-;' region, screened in on the key bezels, will be a keypad layed out sort of diagonally. There should also be an alternate function key like 'Fn' (Toshibas) somewhere. Typically you hold the 'Fn' key down and press one of the FKeys (likesay F11) to activate that keypad... should be in the manual somewhere. Anyway, once you have that pad activated, you can do the Alt + 'character code' like on a regular keypad. Of course, then you have to deactivate it again so you can type normally.
I've mainly used Toshibas, it could be different on other brands, but every laptop I've ever seen had one of those little keypads screened onto the keys.
Hope that helps, good luck.