after new install pc slow down

There can be several reasons why it's slow:
-not enough memory
-graphic driver is not the best one

What kind of computer is it on ? Processor, memory ?
Did you check in System > Administration > Hardware Drivers if there is something available ?

Have you visual effects enabled, then try to turn it off in order to test the behaviour.
system preferences -> appearance -> visual effects = None

Background.
You have two window managers, metacity is standard, compiz is for, lets say fancy behaviour, which needs more resources.

If possible please let us know graphic card and driver.
When uncertain you may open a terminal and post the output of:
sudo lshw -C video

Reference.
https://help.ubuntu.com/community/GnomeTerminal
https://help.ubuntu.com/community/UsingTheTerminal

i have 2gb ram
intel dulcore pentium d cpu 2.80ghz
*-display:0
       description: VGA compatible controller
       product: RV535 [Radeon X1650 Series]
       vendor: ATI Technologies Inc
       physical id: 0
       bus info: pci@0000:01:00.0
       version: 9e
       width: 32 bits
       clock: 66MHz
       capabilities: pm agp agp-3.0 msi bus_master cap_list rom
       configuration: driver=radeon latency=64 mingnt=8
       resources: irq:24 memory:e0000000-efffffff(prefetchable) ioport:c000(size=256) memory:ff5f0000-ff5fffff memory:ff5c0000-ff5dffff(prefetchable)
  *-display:1 UNCLAIMED
       description: Display controller
       product: RV535 [Radeon X1650 Series]
       vendor: ATI Technologies Inc
       physical id: 0.1
       bus info: pci@0000:01:00.1
       version: 9e
       width: 32 bits
       clock: 66MHz
       capabilities: pm bus_master cap_list
       configuration: latency=64 mingnt=8
       resources: memory:ff5e0000-ff5effff

More than fast enough...

Would you mind telling us what is slow ? Is it the boot time ? To move windows? To run a program ? Some examples would be very informative for us. How did you install Ubuntu ? Is it installed on the harddrive, or are you trying it on CD, USB stick, virtual machine maybe ? Thanks !

ive installed on my hard drive using a usb stick
it is slow opening files/programs scrolling though web pages

Thanks François Tissandier, that solved my question.