|"can i install hd 6450 0n x1 slot, if the slot is modded,?"|
As long as you're able to install the card WITHOUT forcing it, it will work. So for example, if you have a slot that's physically x16, but electrically x1, the card will just run in x1 mode. No problem.
"i know pcie is backward compatible, but also heard about some issues on 1.0 versions. can anybody confirm that whether it work or not."
This is kind of a tough one. My PCIe 2.0 Radeon HD 5750 does not work at all on my PCIe 1.0A nForce4 SLI based motherboard*, but works just fine on an i915PM based Pentium M motherboard (also 1.0A).
It looks like the board you have is also based on the i915 chipset, so that video card most likely will work.
*My PCIe 2.0 GeForce GTX 460 card, however, works fine on the nForce board. Hmm.
EDIT: Just noticed this tidbit:
"but before using a soldering iron to my mobo"
No. Not a good idea.
Super PIII | Unlocked ES Tualatin @ 1.8GHz (150x12, 1.65v), 512K L2
3GB PC2700 | 500GB | Radeon x1950Pro | Apollo Pro 266T | Win7 Pro