Some websites are more reputable than others, and some do have little checkboxes for add-ons that you can uncheck to opt out of (and some just slide them in).
Don't feel bad. I've downloaded and uninstalled more times than I can count.
Loretta, yeah, you can even get little portable flash drives that are the shape of a Bic cigarette lighter but about half the size, and they're several gigabytes of space - for $10 - $25!