You can wrap the URL in 'single quotes' or "double quotes" -- The reason to use one over the other is dependant on whether the stuff inbetween the wrapping quotes contains a single or double quote.
For example, if you wanted to use a URL such as:
... then you'd have to wrap the URL with double quotes because "bob's files" contains a single quote. If we wrapped the URL with single quotes, then the code would "breaK" because the apostrophe within "bob's files" would act as the last (or ending) quote:
Likewise, if we wanted to use a double quote in the URL, we would have to wrap the URL with single quotes:
"http://www.yoursite.com/bob said "hi"/ hello.jpg"
'http://www.yoursite.com/bob said "hi"/ hello.jpg'
I do not recommend ever using weirdo characters in any file name or folder name. Try and use only alpha-numeric characters.
The reason I went off on this long explanation is because sooner or later you are going to want to use a file with an apostrophe in your wasp code -- like when you try and reference an FLV video such as:
waspPopup('bob's video.flv', 320, 240)
waspPopup("bob's video.flv", 320, 240)
It will invariably happen, and now you know why.