Apart from the frequent dips, the read speed is about what I would expect for a drive of these specs. The dips may be due to the computer running other tasks, or they could indicate an unhealthy drive.
The Health tab on HD Tune should read S.M.A.R.T. data from your drive (can you post this). It should give you an indication of the health of your drive but I did not find it to be very helpful with the 2 hard drives that failed on me last year.
I had a Seagate 20GB 5400rpm (circa 2002) drive in my father’s computer which failed last December (the contents became corrupted and would not boot). S.M.A.R.T. did not predict this. In fact the overall health which had been at 53% for nearly 3 years went up to 98% afterwards!!! But I had been telling my father for 3 months that the drive was unhealthy because this normally silent drive had become quite noisy when seeking and Windows was noticably slower in general use. But he didn’t listern and so instead of just duplicating his hard drive onto a new one I had to do a complete re-install of everything from scratch . Of couse he also hadn’t used the backup system I set up for him so he lost a lot of documents & photos (I managed to recover most of these, but does he deserve to have have them back :D).
If you have any doubts about the health of your hard drive I suggest that you buy a replacement drive. I would recommend something like a Western Digital WD1600AAJB (160GB single platter PATA Â£32 inc. 17.5% VAT, or the SATA equivalent). The “AA” part of the model name indicates that it is the newer 160GB/platter version. The latest WD drives are very quiet and run a bit cooler than most.