Hi Imran
For opening the xlf in Xcelsius 2008 follow what Jeetan has described.
There is no easy way to converting from Live office to Qaaws. You have build the queries in a way to make the returned data format as close as done in Webi and drop them in the same excel range as where Liveoffice is dropping data now.
But you have to manually build those queries and add the QaaWs connectors.
However, you can still re-use your existing webi blocks by publishing them as webservice - this way you don't re-design your queries or formatting. Then call those Web Service blocks via QaaWs connector. Basically you can skip the building queries and webservices through Qaaws tool by this. For more detail steps