download cc cleaner (free) run cleaner bottom right to get rid of all the junk click on registry after that and scan for issues bottom left when it say do you want save back up etc click yes it saves in "c" drive in case anything goes wrong delete all it finds then click on my computer right click on "c" / properties click on disk clean up.. then defrag your hard drive
that should get you near enough to normal (given there's no faults with the comp)
If you have 1Gb memory thing buy another 1gb.
Its depends for what you use it.
Another think you can check processes in task manager maybe you have opened processes and you don't use them.
Also you can check how much memory process use and close it if you don’t use them.
In system configuration you can close service and programs you don't use but before you do this do restore point (you can delete old all one this give you more memory on hard drive).check your page file size is not to small or to big depends on your ram.