I am looking at going with the 150K service as I surf a lot

, and find a £7.99 increase over my £10.00 little to pay for 24/7 connection.
My PC is as follows;
Intel P3 550MHz CPU,
Intel SE440BX-2 Motherboard,
512K Memory,
Windows XP Home,
2 USB slots (1 used),
No Network connection.
My question is this "Will 150K work OK through my USB connection, or should I;
1. Buy an Ethernet Card,
2. Install it,
3. Mess around getting the drivers to work,
4. Stress out at having to re-activate XP with Microsoft,
or
5. Have a strong coffee, then give up with my 10/100 Card and use the USB."
Any comments would be greatly appreciated.
BTW. I am reasonably PC literate regarding Electronics (HND Electronics and Telecommunications Engineering) and work for a large multi-national Radio Communications company.