Nokia X6 is quite a good choice given by the price. Nokia C6-01 is a better phone IMO, but your budget have to stretch a bit.

For me, i really wished that Nokia have included the Carl Zeiss lens for the Nokia C6-01 phone.

symbian is the OS.. like pc, u have windows, mac, linux, and newly chrome. for smartphones, there is iOS(iphone), android(lots of lots now, look for HTC's, samsung etc), windows mobile 7, and symbian.

ovi is just an account for u. like msn la.. but ovi will enabled u to use all ovi services (again, like google's product also is enabled to be used by registring just gmail. am i rite? ) so, u can download apps from ovi store, used ovi maps..

well, don't expect much from nokia web browser for me, as I'am also jump (not really jump. I ran away) from SE's (I got nightmares using them. maybe just me ). the web browser for me is usable since I also new to smartphone   i suggest u to try nokia X6 16gb as it is within your budget. everything else is pretty well covered IMO but not the part of memory card one.. as X6 didn't have any memory slot
if u really need the memory card, the only options within that budget that i can think of is C5-03. but the camera is not really comparable to X6. plus, the resistive touchscreen (as on older touchscreen phones. like 5800, which used the stylus) vs capacitive on X6 (capacitive is like iphone simply put.. very responsive compared to resistive. but will never respon to normal stylus and fingernail)

but if u may have any chances to extend your budget, better get new symbian^3 devices such C6-01 for smoother UI (compared to X6). it covers all your need there by topup around 100