Agree with the above regarding,celeron slow as crap & getting a faster hdd & add more ram,you also need to take into consideration auto start programs you don't need or at least switch them to manual start,this can be done with services.msc while others with ccleaner or msconfig
i.e
bluetooth service
Any image backup service excluding system restore
wmp network share (do they still make wmp)
windows update
adobe
fax (nobody uses this anymore except maybe jafo)
print spooler (windows printer driver service)
edit:
forgot to mention installing a distro of linux in dual boot wouldn't go astray,puppy 64bit or even the 32bit versions are super fast as they can run fully ram if using a cd & just as quick from hdd.
distrowatch has plenty of versions of linux you'll most likely be ok with a kde,debian or gnome desktop version.The xfce versions are considered lite with the extra crap removed & the Mate versions are for older hardware