Multitrack recording with USB 1.1

I intend to purchase a sound card for my notebook (USB connection). It will
be used for multitrack recording of voice (mic in) and electronic
instruments (line in).
After reading several postings in this newsgroup, I have three questions.

1) In one article I found the hint that not all units support simultaneous
playback and recording (which is essential for multitrack recording). Can
anybody tell me whether Creative Labs Extigy or the Sound Blaster MP3+
support this feature ? (I would prefer the Extigy because it has MIDI
connections too.)

2) Is simultaneous stereo playback and recording possible with USB 1.1 or
does it compromise sound quality (I want to record with 44,1 kHz) ?

3) Do you have any other recommendations for me (the unit should support
Win98SE) ?

Thanks in advance for any answers.
Eberhard