Hej
Yes, an Athlon 64 X2 Dual-Core will be much better than the CPU you have now.
The best CPU you can use with your current motherboard is an Athlon 64 X2 Dual-Core 4800+.
A8N-E CPU support:
http://support.asus.com/cpusupport/c...us&model=A8N-E
But, that CPU is VERY expensive in Sweden.
The Athlon 64 X2 Dual-Core 4200+ costs about SEK 1500-1600 (expensive, IMHO - but maybe you can find it cheaper).
http://www.prisjakt.nu/kategori.php?k=s18318550
PSU:
http://www.prisjakt.nu/produkt.php?p=109370