Advice about external hard drive........

Hi there.....

I run some special programs, and want to be able to use my laptop, as some times I need to be mobile with them, but they are quite big, and make the laptop really slow. As I cant afford to get another laptop, I was thinking, if I got an External Hard Drive, had the programs installed on there, that I would be able to access them and use them from my laptop if the external Hard Drive was plugged in to the laptop, with out slowing the speed of the laptop down.

Would I be able to do this with an External Hard Drive?

I asked my son, but he wasn't sure, he said he thought part of it could be used for extra memory for the laptop to make it run faster, but he wasn't sure if I could have programs on there and access them and use them from my laptop too.....
He also thought that I would prob have to up-grade to Vista before I could do anything.....
Could you let me know please?

I have been looking at some on eBay 300/400/500 MB ones, they also can have extra USB ports on them if you want them too.....

I am just not sure if this is the right way to go, for what I need to do, any advice would be appriciated please.

Many thanks for any help in advance

you could go for an external laptop HDD - u get a 120 Gb drive for around 4K
(if space is the constraint )
U could install the application on the HDD and plug it in when u need to use it.

But i'm not sure if the size of the programs is making it run slower. It could be that you have insufficient RAM.So if u have enough hard disk space , consider upgrading the RAM.