In Dolphin, open the settings (app settings button->More>Settings)
Expand the menu item for "Dolphin settings"
Look a few items down in the menu, and select "User Agent"
Select the radio button for "Custom Agent"
Enter this string: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)
That is the user agent string for IE7.
The browser will send that string in http requests to the site, and you should be able to at least open the page. Functionality may be limited if the site really requires Windows support, such as ActiveX.
Update: Valkillmore (post below) discovered that the site of concern to nashantmaniya works with Opera. Apparently that site does not like Mozzilla/5.0 UAs, or some other part of those UAs. Maybe it acepts Opera or Presto UAs. Whatever.
The point here is that if future readers of this thread encounter similar issues with browsers, and do not wish to install a bunch of different browser apps, and then have to rely mostly on luck to determine whether one or the other might work, then the following Android browser UA information may be useful. Dolphin allows you to set any user agent that you wish, so if you want to make Dolphin masquerade as Opera, you could use the UA for Opera, etc. I have shown above how you can make Dolphin masquerade as IE7.
And finally, to make this subject a little more relevant to the a500 forum. Look at the UAs below to see how easily certain websites (those that are interested in providing customized/special content) can detect that you are browsing with an a500, Tablet, etc. when you use some browsers.
Android Browser User Agents
Opera User-Agent:
Opera/9.80 (Android 4.0.3; Linux;Opera Tablet/ADR-1204201824; U;en) Presto/2.10.254 Version/12.0 0
Stock Android browser User-Agent:
Mozilla/5.0 (Linux; U; Android 4.0.3; en-us; A500 Build/IML74K) AppleWebKit/534.30 (KHTML,like Gecko) Version/4.0 Safari/534.30
Stock Android browser (request desktop) User-Agent:
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/534.24(KHTML, like Gecko) Chrome/11.0.696.34 Safari/534.24
Google Chrome Beta User-Agent:
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.45 Safari/535.19
These are the Dolphin built-in UA choices:
Dolphin (Android) User-Agent:
Mozilla/5.0 (Linux; U; Android 4.0.3; en-us; A500 Build/IML74K) AppleWebKit/534.30 (KHTML,like Gecko) Version/4.0 Safari/534.30
Dolphin (desktop) User-Agent:
Mozilla/5.0 (Macintosh; U;Intel Mac OS X 10_6_3; en-us) AppleWebKit/533.16 (KHTML, like Gecko) Version/5.0 Safari/533.16
Dolphin (iphone) User-Agent:
Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_0 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A293 Safari/6531.22.7
Dolphin (ipad) User-Agent:
Mozilla/5.0 (iPad; U; CPU OS 3_2 like Mac OS X;en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4 Mobile/7B367 Safari/531.21.10