As u knw tht i wanna ugrade my PC which hv only PATA ports.
As per ur reply tht External USB Hard Disk is not better for me as compare to SATA Internal/External HDD.

Now i hv heard about eSATA...,is there any difference b/w SATA n eSATA n which one is better for me amng thm as per requirements of my OLD P-4 1.5 PC with 384MB SD PC133 RAM.

Is there any Difference b/w SATA n eSATA PCI Cards?
If i would buy eSATA PCI card thn which HDD i need to buy( SATA or eSATA)

The drives are the same, the e if for external. See What is eSATA?

sir please tell me one more thing does sata pci card supports esata drive or should i buy sata drive or esata drive and please list some best hdd and pci sata or esata cards . please suggest the best one to me.

and can my pc support 1tb hdd my pc config is compaq presario series 5000 5610ap p4 1.5 384 mb ram intel 845g processor

The drives are the same and it should support your a large drive - but you may have to divide it up into smaller partitions. You need to see if the BIOS supports 48-bit LBA.

That said, with only 384 Mb of RAM, performance will never be good.