I have an AMD Sempron 2800+ processor on a C51G-M754 motherboard, 512 MB RAM.
I intend to upgrade my processor to An Athlon64, which model do you suggest?
thnx in advance… 
It is not so much what would we suggest, but what the motherboard and its BIOS supports as it is entirely possible that any suggestion might not be supported by your motherbord and BIOS.
Also the reason why you want to upgrade your CPU would assist in the choice made.
Are you sure that is the motherboard you have http://www.hardwaresecrets.com/article/289, if so you would be looking at the best that it can support at whatever price you can afford. I would suggest that you upgrade your memory as that is likely to give a boost depending on what applications you run.
The on-board graphics are also nothing to write home about so if you are doing any graphics intensive work than a decent graphics card would also help.
Your CPU is Socket A, Athlon 64 is using Socket 754 or 939. So you’ll have to replace motherboard too.
If you do intend to upgrade everything look at Athlon64 X2 6000+ or something from lower end of Core 2 Duo segment.
These are quiet cheap now and pack some punch for games and even work. Memory shouldn’t be below 1GB these days.
If you don’t need fancy graphic card, take motherboard with integrated one, otherwise GeForce 7300GT/7600GT is still a very cheap and decent card (though don’t expect too much from it). For more look at GeForce 8500GT or Radeon x2600 Pro.
Everything is per your need.
The motherboard according to the URL in my post is socket 754 as seems clear by the motherboard ID/model number C51G-M754. The CPU came in different architectures the early ones being socket A the later ones socket 754.
http://www.driverheaven.net/reviews/Sempron/
The Sempron comes in 3 varieties, on the desktop there are Socket A and Socket 754 models. On the Mobile side there are Sempron’s based on Socket 754. Our Sempron review sample is a Socket A 2800+ clocked at 2Ghz where as a Thoroughbred Athlon XP was 2800+ clocked at 2.2ghz. The Sempron FSB is running at 166MHz (333 MHz effective) as the Thoroughbred also did and really, that’s all you need to know about the CPU.
So it would seem the CPU and motherboard are socket 754
Nevermind, i missed the name Sempron…
These days you might find it hard to an AMD64 for 754 socket since they are now a few years old. For a faster Sempron check this link and scroll down. Notice as you scroll down, there are no listings for AMD64 in the 754 socket.
http://www.tigerdirect.com/applications/Category/category_cpu.asp?name=CPUs
But then, I did find one listing here at the top of the page so they are getting hard to find. They only have 102 units in stock. If you want one, son’t wait long or they will be gone. It is a AMD Athlon 64 3200+ 512KB Socket 754 CPU.
http://www.pacificgeek.com/showcategory.asp?c=201&s=1073
As you are in Egypt, I do not know what the shipping cost would be but the unit price is very good at both sites.
many thnx