Chinese BIG5 to GB gateway. How?

Hi, anybody has experience about making a webpage in Chinese Big5 but it can be converted into GB format by user request? I heard this function required chinese big5 to gb gateway installed on server but they all cost expensive. is there any way for free? Thanks.

When you say converting do you really mean translating from GB to BIG5 on-the-fly?
Are you being lazy or having problems creating two versions of every page?
I'd say if you are from the mainland just use GB all the way, why bother with BIG5?

Thx freebsd, but that's not a static page. it's a forum like bullet board in big5. I also need to make the page in GB version as well. for chinese, BIG5 is good for HK people and Taiwanese but GB is only good for people from china. Headache.....

Then set your default charset to Big5 and for those who can't read tell them to install traditional chinese language for their IE or whatever browsers.
You, being the administrator or site developer, just can't worry too much about client-side issues. Your duty is to send the appropriate (preferably big5 as the default) charset as simple as:

<meta http-equiv="Content-Type" content="text/html; charset=big5">

If I were you I wouldn't bother with GB just because Simplified Chinese is non-standard and many Chinese (I'm one of those) can't read it.