why is Flight Gear so slow?

[Douglas Alves]

I installed FGFS and its dependencies from Warty's universe, but when I
start it up, it functions in an intermittent manner: sound and movement
for 2 seconds, silence & stillness for 2 seconds, and so on.

My desktop's characteristics: (kernel 2.6.8.1-4-686)

RAM: 256 MB (32 Mb integrated video)  DDR333

# fdisk -l

Disk /dev/hda: 40.0 GB, 40020664320 bytes
255 heads, 63 sectors/track, 4865 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

 Device   Boot Start   End    Blocks   Id  System          Used/cap Gb
/dev/hda1   *      1  1025   8233281    7  HPFS/NTFS        4.7/ 7.9
/dev/hda2       1026  2983  15727635   83  Linux            2.9/15.0
/dev/hda3       2984  4600  12988552+   c  W95 FAT32 (LBA)  3.6/12.4
/dev/hda4       4601  4865   2128612+  82  Linux swap         0/ 2.0

# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Intel(R) Celeron(R) CPU 2.50GHz
stepping        : 9
cpu MHz         : 2488.334
cache size      : 128 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid
bogomips        : 4915.20

What am I missing?  What's going wrong?