There's no native Java support on the N900, so those sites won't work through the default browser.
However, you might like to give Opera 10.x a try. The developers wrote their own custom Javascript engine for it. The applets might work in that.

I'm actually looking at the HDFCSEC log-in/sign-up page on my N900. But I was told I need IE 5.5 to view the sites, but I just tapped OK and the page loaded anyway.

Hope that helps.