MSI Lightning GTX 260 1792MB SUPERCLOCKED to gtx 465 worthy upgrade?

There will be a difference. It will not be perceptible. Save your money.

how much difference in fps?

According to guru3d's chart for Crysis Warhead at 1900 resolution... 1.

i meant the difference between gtx 465 and my lightning 260

Guru3d benchmarked the MSI Lightning 260 right about the same as the GTX275, so I used that as a stand-in. The chart says a GTX 465 averages 1 frame per second faster than a GTX 275.

plz give the link to the review

The fact is GTX465s are all not worth it (maybe not the MSI gold version, but unlocking is risky), runs hot, sucks power while performs miserably. Get a GTX470 if you want, its only like $50 more.

Here's the review for the one you have now: http://www.guru3d.com/article/msi-geforce-n260gtx-light...
Here's a page with a chart(ignore the 2 orange bars) showing the GTX 275 and GTX465: http://www.guru3d.com/article/msi-n465gtx-twin-frozr-ii...

k.so the 465 is just around 1% faster than my card.Might as well stick to the 260

Save the cash, that's still a potent card:

http://www.tomshardware.co.uk/geforce-gtx-460-radeon-hd...

Both Crysis Warhead and Metro 2033 have stratospheric system requirements, even at medium resolutions-Merto 2033 is practically uplayable on my rig under DX11, even at lower resolutions for example (although its smooth under DX10).
Probably your best option is to SLI a second GTX260, the only other upgrades that will give a worthwhile boost take you into GTX480/HD5870 terratory.

but if i dont upgrade will the 260 max out all the other games other than metro crysis(dx9)coz i m on xp.

Game system requirements continue to rise but your existing card should play all of them at at least 1650x1080 at or near to maximum settings.
Upgrading to a DX11 card with XP is a total waste: The newer cards are little faster than your existing one, and will still give you DX9 visuals-DX10/11 cannot be used under XP. If I were you, I'd think about migrating to Win 7 first, at least that way you'll get full value from the existing (DX10) GTX260.