The Blackberry browser is a far cry from what you will see on your desktop browser. In most cases you are either going to see a very poor rendering of the standard HTML site or a WAP version (if the site caters to handheld users). The HTML version will be very bad, and is usually close to unusable. The WAP version will often be a stripped down modified version to make it easier to get around on the site via handheld.
In all cases, Flash media will be removed/ignored by the browser which will only add to the mess, since so many sites have flash content and fail to properly setup alternate content.
If the browser is really important to you, you have a few options:
1.) Install Opera Mini on your Blackberry
2.) Purchase a Blackberry that is capable of running OS 4.6+ (much improved Browser, but not perfect)
3.) Purchase an alternate device that has a premier browser, usually a WebKit based browser. iPhones are an example of such a device.
Hope this helps.