C 255 Characters

x=8,y=8,T,p=1,i,j,N[17][17]={0},a[]={0,1,0,-1},b[]={-1,0,1,0};c(t){p=(p+t+4)%4;x+=a[p];y+=b[p];}main(){scanf("%d",&T);while(T--)N[x][y]=(N[x][y]+1)%2,c(N[x][y]?1:-1);for(;i<17;i++)for(j=0;j<17;j++)printf("%c%s",i-x||j-y?N[i][j]?'#':'_':'@',j-16?"":"\n");} 

http://ideone.com/VnOcq

C 195 Characters

x=144,T,p=1,i,N[289]={0},a[]={-17,1,17,-1};c(t){p=(p+t+4)%4;x+=a[p];}main(){scanf("%d",&T);while(T--)N[x]=(N[x]+1)%2,c(N[x]?1:-1);for(;i<289;i++)printf("%s%c",i%17?"":"\n",i-x?N[i]?'#':'_':'@');} 

http://www.ideone.com/Dw3xW

I get this for 725.

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