NO! Get a new system... Packard Bell is the WORST PC maker ever (well, ok maby not the absolute worst). Depending on the model it is very hard or impossible to upgrade as they used many non-standard things (cases, form factors, power supplies, motherboards... yadadaa). Even if this model has standard AT components you are still stuck with crummy options. You will only hurt yourself in the long run trying to upgrade it... it's too old to begin with, and Packard Bell sinks the deal.
Save up some money and get a cheap barebones:
Duron MB with integrated video/sound ~$75, 600mhz Duron ~$40, 128bm PC133 ram ~$30 after rebates, 20GB HD ~$30 after rebates, cheap case/250watt+ power supply ~$50 (or less, but I'd go with $49 Antec to insure a good power supply), use your existing monitor/mouse/keyboard/CD/Floppy ==== kick butt system for $225 or so. Shipping will probably be around $30 unless you live in a city with chain stores like Fry's that you can grab the parts from on the cheap. ALso keep an eye out for barebones AMD duron systems, case/ps, MB, CPU for cheap...
Good luck...
Brad