With XP, 128MB RAM is bear minimum and you would be choking the system.
Like a drag race with only a pint of fuel in your drag.
Your computer overall speed, and speed of every action, even opening any application such as IE, will need RAM and CPU mainly. You'll see
ALOT of improvement in everything if you were to upgrade to 512Mb and I certainly would recommend it straight away.
With IE download and upload speed, 4.5Mbit/s connection is download. Your upload is probably 512Kbit/s or something lower most likely. That would making uploading anything pretty slow but downloading would be pretty fast and so would internet speed.
8Bit = 1Byte
So your download would be a maximum of 562Kbyte/s. Most net connections work at a threshold of 80% of the ad value, on average, so you would be getting 450Kbyte/s download.
Not fast, but not slow either.