Will do Millie1.
I think to be honest, that the 350D SLR and the IXUS 4 /5 / 700 are very different beasts. The Ixus being much smaller and lighter is more what you grab for a quick snap, a no-brainer to take on holiday, a point and shoot; the SLR is significantly larger and heavier, so not for the handbag, but it will allow you more control over your photography, the ability to select longer / faster lenses if you need higher power zooms, and of course the ability to more easily get creative with aperture / shutter priority etc.
If budget is limited with regards to an Ixus, I think you might want to go for a cheaper 4 / 5 MP model as the increase in resolution probably isn't, really, needed for your photos. Looking at snaps on a PC / laptop or in 6X4 or 7X5 prints doesn't need 7 / 8 MP, as I'm sure you're aware.
If budget is limited but you feel an SLR would be best, perhaps you would be pleased with the older EOS300 which I imagine will be available much cheaper as people opt for / upgrade to the EOS350. Similarly, the Nikon D70 has now been surpassed by the new model (is it the 70D ? and the new D50 too I think) so that too should be available much cheaper pretty soon.
Also I guess consider the availability / cost of any lenses you might need... do you already have any Canon / Nikon glass ? A 70 -200 won't exactly be cheap, especially if you want fancy image stabilisation etc. etc. etc.