Ubuntu comes by default with its defult Desktop GUI enviremnet that will can be very heavy for an old PC, therefore I wold install only Ubuntu server and manually install a light Desktop environment

Type the following command at the Terminal Command Box:

sudo apt-get update

to install XFCE :

sudo apt-get install xubuntu-desktop

alternatively, you can also try LXDE instead of XFCE by the following command:

sudo apt-get install lubuntu-desktop

After the above installation you need to reboot your PC

In your Ubuntu machine (mine is 12.04 version), type the following command at the Terminal Command Box to install the xrdp

sudo apt-get install xrdp

Now in your Windows machine, go to Start –> All Programs –> Accessories –> Remote Desktop Connection and type the IP address or HostName of the Ubuntu machine then click‘Connect’

When prompted, enter your Ubuntu username and password and click ‘OK’

Now you should see your Ubuntu desktop

Following procedure will help you to free more memory in ubuntu machines :

Type the following command at your terminal command prompt :

1. Check the current memory
   

   free -m

2. Flush file system buffers for safety
   

   sync

3. Become root (simply sudo-ing the final command won’t work because of the redirection)
   

   sudo bash

4. Free cached memory
   

   echo 1 > /proc/sys/vm/drop_caches

5. Now finally check the memeory status after freeing
   

   free -m