Change visible property on an event

[Guest]

Hello,
I'm using vstudio web developer exp. ed. and i want to know how can i change
the visible property of a webcontrol (for example an "Image" control) on an
event occurence (for example "onmouseover" event).

thanks for reading this silly question.Actually i'm not aware of client
scripts.If you can suggest me any site that gives some information & sample
codes of these sripts i'll be gratefull to you.