Maximum number of USB ports?

Right now I'm having trouble on my RAM, I'm still using ACER travelmate 260, and it's hard to find cheap SDRAM these days. because of that I'm thinking on using flashdisk as virtual memory, but I'm a bit concern how many USB ports a computer can handle.

My laptop only has 2 USB 1.1 ports and 2 USB 2.0 ports (via PCMCIA), I have plan to buy usb ports extension which virtually makes me have 5 USB 2.0 Ports and 2 USB 1.1 (7 totals). Is this safe for my computer? I heard that it is not recommended to add more than 6 ports in USB, so I'm really wondering if someone could confirm me about this.

Jam it back in, in the dark.

Actually, I'm only using one USB 1.1 port to power the PCMCIA, and using the two USB 2.o ports for external HDD, printer and DVD-RW. Of course I dont use it simultaneously all the time, I only plug the HDD and DVD-RW when I need to burn though, is it still considered safe? Perhaps there will be times when I will use three ports in same time (for hardisk, dvd-rw, and usb flashdisk).

How ya doing, buddy?