@Anoop: You need to access Picasa Web Albums in order to upload your images and view them online. You can do this either thru the Picasa client or by going to the site and manually uploading your pictures.
All this means is that you need to have the images uploaded to Flickr on your hard drive.
There is a multi-file upload mechanism but it is only available as an ActiveX control for Internet Explorer. More details here.
UPDATE: After some searching, I came across Migratr:
Migratr is a desktop application which moves photos between popular photo sharing services. Migratr will also migrate your metadata, including the titles, tags, descriptions and album organization. Whether you want to copy your photos from Flickr to Faces, Picasa to Phanfare, or Zenfolio to Zooomr, Migratr is the app for you. Migratr will copy your photos FROM any supported photo service, TO any supported photo service.
Currently, Migratr supports the following services:
23HQ
Aol Pictures (Import Only) (CLOSING)
Faces.com
Flickr
Menalto Gallery (Self-Hosted)
Picasa Web
Phanfare
Photobucket
SmugMug
Zenfolio
Zooomr
Hope this helps!