my pc is dog poo

spec

intel celeron cpu 2.7
256 of ram
s3 pro savage gfx card




can i just change my gfx card, add more ram and change the cpu processor?

and this would bring my pc closer up to date?

or is it a can or worms? will i need a matching motherboard with the cpu processor?

also i looked up processors on ebay and some come with gfx card built in??


id like to upgrade myself and get some experience
any info would be great