As has been correctly suggested, you are at the very low edge of usability in terms of on-board RAM. All the specs (and some experts!) will tell you that 1GB is perfectly sufficient to run Windows XP - and they're right, so long as you don't want to do anything useful with it! But for anything which requires real processing power, it really isn't sufficient. The slowness is likely to be the machine actually running out of real memory and being forced to use part of its hard disk as "pretend" memory.
Luckily, according to various sites, the machine's on-board memory can be upgraded to 4GB:
http://www.orcalogic....Memory-35060-m-1.htm. I'd suggest you do that.
You should also download and run malwarebytes just to make sure that the machine hasn't picked up any malware which is taking over the machine at various times.
Finally, I'd suggest getting one of these:
http://www.maplin.co....off-airduster-345490, powering the machine off, taking it outside, removing as many of its panels as you can and giving its innards a good blast, especially the fan(s).