i want to save/open a file in txt format other then CSV in SSRS 2005. So any one who knows how to add file extension in url that can overirde default extension in SSRS 2005..
I think you mean you want to export a report to a text file, but not CSV format? You haven't specified what other format you want, but if you want to output to a text file with a different kind of delimiter (for example Tab or | ) then you can do that by rendering the report via URL Access and overriding some of the rendering extension parameters.
For example, to export to a TAB delimited file with the extension .TXT:
http://SERVERNAME/reportserver/?%2fReportFolder%2fMyReport&rs:Format=CSV&rc:FieldDelimiter=%09&rc:Extension=TXT
As far as I can tell SSRS 2005 does not support setting these values in rsreportserver.config unfortunately. However SSRS 2008 does, which means in 2008 you can create a new rendering extension based on CSV and specify these settings. Users can then select the render format from the Export list in Report Manager, however as I mentioned 2005 does not support this so I think URL Access is your only option.